When I first used Slack back in 2015, I could not for the life of me wrap my head around the concept of threads. Now, after a decade or so of Slacking, I'm the person passive aggressively reminding people to please respond in threads for the love of all that is productive. That's all to say: I know what it's like to completely not understand Slack—but I also know enough to help you understand it.
The short version: Slack is a team chat app that organizes conversations into topic-based channels. Teams use it to chat, share files, and even hop on quick calls. At Zapier, our internal communication is done almost exclusively in Slack—it's completely replaced email for us.
If you haven't used Slack before—or if you've used it for years and still don't know what a thread is for—this guide covers everything you need to know before diving in.
Table of contents:
What is Slack?
Slack is a team chat app built for workplaces. Instead of sending an email to six people and waiting for the reply-all chain to begin, you post in a channel—things like #marketing, #product-launch, or #fun-ai—and everyone who needs the context can see it. Everyone who doesn't can mute the channel and move on with their day.
Slack also handles file sharing, voice and video calls (which Slack calls huddles), searchable message history, and native connections to thousands of other apps.
What is Slack used for?
If it were up to me, Slack would replace every inexplicable combination of single-purpose apps teams have cobbled together for communication. Until then, here's what it looks like in practice:
Communicating in public channels: We focus on transparency at Zapier, so we try to do most of our work in public channels. There's always a #general channel, which is for company-wide communication. Other channels are usually organized by team (like #marketing, #support, or #partnerships) or topic (like #okr, #q4-launch, or #competitor-intel). Channels can be public (anyone can join) or private (by invite only), and within channels, you'll communicate using threads, so each conversation is easy to follow.
Sending direct messages: Some messages are better kept private—like following up with a teammate about their PTO request or practically any question to the HR team. DMs let you communicate directly with one person or a small group, and no one else can see those messages.
Audio and video calls. Slack huddles let you join a one-on-one or group call—audio-only or audio and video—with just one click. So instead of "spinning up a Zoom" for a 30-second question that's easier answered IRL, you can just do a casual huddle. It's not a full Zoom replacement, but huddles have all the basic video conferencing features you need for a quick sync, like screen sharing and the surprisingly effective Raise hand tool.
Alerts from other apps. Slack can receive messages from the tools you already use, so if a new lead is added to your CRM or there's a failed payment in Stripe, you'll be alerted in Slack. You can even turn a channel into a live feed of whatever you need to know about. And if you connect your Slack to Zapier, you'll get integrations with 9,000+ apps, so Slack can be your source of truth.
External communication. If you're working with external stakeholders, Slack Connect makes it easy to keep your communications in Slack, while limiting their access to only the channels you invite them to.
Slack is also pretty popular for online communities (it actually started as a way to chat while gaming online). Plenty of hobby groups, alumni networks, and professional communities run on it.
How does Slack work?
This section gives you an overview of how Slack works and its key features. For a beginner's guide on using the app, step by step, check out Zapier's guide: How to use Slack.
When you open Slack, you're in a workspace, which is the home base for a company or group. (If you belong to several workspaces—for example, one for your company and one for a community you're a part of, you can click your workspace profile picture at the top of the sidebar, and select another workspace to switch to.)
From there, the best way to understand how Slack works is by diving into the key tools and features you're likely to use on a daily basis.
Slack channels
Any new team or topic, no matter how niche, can have its own channel. To give you a sense, we have over 3,500 channels at Zapier—and that's after we've done some cleanup. Click the channel name to view the channel description and member list. From there, at the top of every channel, you'll find tabs for messages, canvases (Slack's shareable documents), a button to start a huddle, and shared files and links. You can customize this further and group those shared files into folders or pin specific messages. (For a deeper look at setting channels up, see our guide to creating and managing a Slack channel.)
If your Slack channels or DMs fill up with new messages faster than you can say "hummus" (IYKYK), you can also use AI to summarize the messages for any given time period. I'd take the summaries with a grain of salt, though. In my experience, they're still pretty hit or miss. (AI features in Slack are limited to paid tiers, so if you don't see the feature, that's why.)
Slack threads
When someone posts in a channel, any replies go in a thread—or, at least, they really should. (If they don't, I send it back.) Threads keep replies tidy: when you reply to a message in a thread, the response is tucked under the original instead of bumping every other conversation up the channel. You can still use @mentions to get someone's attention, but they won't get notified about replies unless they reply to the thread or they specifically request to get notifications from that thread.
Slack reactions
Just like on a text message, you can react instead of responding. Use a 👍 in place of "got it," 👀 to indicate that you're following along, or 💯 to show appreciation. You can also add custom emoji: we have over 22,000 (not a typo) at Zapier—more than a small percentage of them are AI-generated images of my dog on various forms of transportation. Slack reactions can even kick off automated workflows. For example, you can set up a workflow in Slack's Workflow Builder so that when someone adds a 🙋 reacji to a message in #help-requests, Slack automatically sends the person who reacted a form to log the request, then posts the details to a tracking channel.
Slack search
Unlike with email, where you can search only your own archives, Slack lets you search for anything—as long as it's shared in public channels or in private DMs with you. If you click into the channel where you think your search item is hiding, Slack will automatically narrow its search to that channel.
But you can get more specific with multiple filters. For example, #in:team-content from:@deb has:link will retrieve any message I've sent that includes a link in the #team-content channel. (Note: Slack's free plan only keeps 90 days of message history searchable, while paid plans keep everything.)
You can also search using natural language—for example, "What's the latest status on setting our Q1 goals?" Slack will give you its answer, along with links to any Slack messages or files that informed its response. (If you're on an enterprise plan and you can't see AI answers, your admin may have disabled this feature.)
Learn more: How to use Slack search
Slack huddles, clips, canvases, and lists
Slack also has a few extras that mean you don't need to leave the app for every little thing:
Huddles are quick audio-only or audio and video chats that you can start from any channel or DM, with screen sharing included.
Clips let you record a quick audio, video, or screen recording and drop it in a conversation.
Canvases are shareable documents that live inside Slack, handy for meeting notes or project briefs.
Lists help you track tasks and projects without leaving your channels.
Slackbot (personal AI agent)
Slackbot started out as a simple bot for reminders and canned replies, but it now works as a personal AI agent that can help you put together reports, build automations, create dashboards, summarize threads, or take actions across your connected apps.
Slack integrations and apps
Slack can be your communication hub and source of truth, but chances are, it's far from the only app you use—which is why Slack gets more useful once it's connected to the rest of your tech stack.
The Slack App Directory has more than 2,600 apps, including Google Drive, Jira, Salesforce, and ChatGPT. You can use those integrations to share files, preview links, start a task, or receive alerts straight in Slack. We've rounded up the best Slack apps if you want to see what's worth installing.
Slack also has a built-in tool called Workflow Builder for no-code automations inside Slack, such as an onboarding message for new channel members or a form that routes requests. On the free plan, you can install up to 10 apps, and paid plans remove that limit.
Slack MCP lets AI tools like Claude and ChatGPT search your messages, read channel history, and post on your behalf, so you can ask an assistant to "summarize what happened in #launch-planning this week" without opening Slack.
But Slack MCP only covers Slack. If you want an AI assistant to work across the rest of your tools too, you'll need something that reaches further. With Zapier, you can securely connect to 9,000+ apps and set up automations that run in the background while you work. For example, you can post a Slack message whenever a new lead lands in HubSpot or create a Jira ticket when someone reacts to a message with an emoji. Build from wherever you work, and it's all governed from one place.
How much does Slack cost?
Slack has a free plan and three kinds of paid plans.
Plan | Price per user/month (billed annually) | Price per user/month (billed monthly) | What you get |
|---|---|---|---|
Free | $0 | $0 | 90 days of searchable message history, up to 10 apps, one-on-one huddles |
Pro | $7.25 | $8.75 | Unlimited message history and apps, group huddles, AI conversation summaries |
Business+ | $15 | $18 | Everything in Pro, plus Slackbot, AI search, daily recaps, and file summaries |
Enterprise+ | Contact sales | Contact sales | Advanced security and admin controls, plus enterprise search |
The free plan is a good way to see whether Slack fits how your team works. You get channels, direct messages, search, and Slack Connect for one-on-one messages with people outside your company. The most important limits you'll bump into are the 90-day message history—which, IMO, kind of defeats the purpose of Slack—and the fact that you can't do group calls.
On paid plans, you'll get unlimited message history and apps, plus access to group huddles, and more AI features. If you're planning to use Slack as your internal communication tool, it's absolutely worth paying for.
What is Slack? FAQ
You've probably got more questions about Slack. I've got answers.
Why is Slack so popular?
I'd argue it's because Slack made workplace chat feel casual. It's also a lot of people's first experience with team chat—and the first time you use it, it feels revolutionary, especially if you're only used to email.
Is Slack free?
Yes, Slack has a free forever plan. The main limit is that it only keeps 90 days of message history, which takes away a lot of the value Slack offers to begin with. The free plan lets you install up to 10 apps and limits huddles to one-on-one. Paid plans start at $7.25/user/month (billed annually).
What does Slack stand for?
According to co-founder Stewart Butterfield, Slack stands for "Searchable Log of All Conversation and Knowledge."
Who owns Slack?
Salesforce has owned Slack since 2021, when it acquired the company for about $27.7 billion. Slack still operates as its own product, but it's increasingly connected to Salesforce's CRM and AI tools.
Is Slack only for work?
No. Many people use Slack for hobby groups, volunteer organizations, and online communities. The free plan works fine for those, though the 90-day history limit can be annoying if you want to look back at older posts.
How do I get started with Slack?
Go to Slack, create a free workspace, make a channel for a real project, and invite a few teammates. Learn more about how to use Slack.
Why use Slack instead of texting?
Group texts are one endless scroll, ideally overrun with dog pics. Everyone sees everything, which means there's no way to separate different topics, and important things (see: dog pics) get lost among less important things.
Slack fixes this with channels, so each topic gets its own space, and with searchable history, a new person can read up. It also keeps work off your personal phone number, and you can set notification schedules or snooze alerts so a coworker's question at 9 p.m. your time can wait until morning.
How is Slack different from email?
Email isn't dead, no matter how many headlines claim it is. I still use email to communicate with freelancers, and it's the best channel for marketing messages and cold outreach. But Slack is better for the fast back-and-forth, such as quick questions, ongoing projects, and the dozens of small decisions your team makes in a day. Plus, it's searchable to everyone—not just the folks on the thread. And Slack has a million features email doesn't, and some that email does but shouldn't (hello, emoji reactions).
Is Slack like Microsoft Teams?
Yes! But also no. Slack and Teams are both team chat apps, and they overlap a lot. They both use channels and threads, so the core of communication is the same. The three main differences are that Teams adds an extra layer of organization (teams, which are then divided into channels), Teams has better video conferencing features, and Teams is deeply tied to the Microsoft system. If any of those things matter to you, it's worth a look.
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