Getting started with the email app on Zapier is actually quite simple. Because the email app is provided in-house by Zapier, you do not need any sort of special Account to get started.
When you use the email app to receive email, you'll be given a special @zapiermail.com email address. This email address is unique to the Zap. You should modify it further by typing in a prefix, like "mike".
To trigger the Zap shown in the screenshot, you would send an email to firstname.lastname@example.org.
This action will send an email from Zapier for you. All emails will come from a no-reply email address such as email@example.com. Accounts are limited to 10 emails per hour using this action.
When sending emails, you can specify to, subject, body, from name, attachments, reply-to, cc, and bcc.
If you need emails to come from your own email address you should use one of the "high volume" email apps.
All emails sent from Zapier also include a "stop Zap" link at the bottom of the email to prevent spam. If the link is clicked, the Zap which send the email will be turned Off. This is atypical to how most "opt out" lists work where only the specific user who opted-out is removed from further mail.