When you edit or create a new Appointment Type, the first couple of options you'll have are Duration and Padding.
Duration is simply the length of your Appointment Type. Set the duration to 30 minutes, for example, and that's how long the appointment will be.
Padding ensures that your appointments won't be scheduled too close together; it puts in some breathing room between when one appointment ends and the earliest time that the next one can begin. Padding is one factor in which spots are open for your clients to be able to book themselves.
For example, you might use 10 minutes before a weekly coaching call to get up to speed on the client, and then 10 minutes after each call for note-taking from the session.
Together, Duration and Padding determine the total amount of time that is blocked off in your calendar for that appointment type. In the example below, the total amount of time blocked off for this appointment type would be 50 minutes.
30 minutes for the session
+10 minutes padding before the session
+10 minutes padding after the session
50 minutes total must be available