A buffer is used when building out a Scheduler to give yourself time before or after a session. This is to prevent back-to-back sessions on busy days.
To set up a buffer on your scheduler, you first need to either create a scheduler or edit one. Go to Overview > Schedulers > Add New or click on one of your schedulers to edit it. Go to the "Advanced Availability" section to find the buffers. Two options will be available to you to set:
Buffer Before Events, which is how much time you want in between sessions before an event.
Buffer After Events, which is how much time you want between sessions after an event.
You can choose between 15-minutes, 30-minutes, or one hour, or set a custom buffer time for both options listed above.
Why can't I see the buffer on my availability?
Buffers were meant to be used in conjunction with the Availability Increments section. A buffer will not change your increment settings. It will only block off the slot before or after a session (depending on the buffer set).
If you want to change the slots available to your client, you'll need to factor it into your increments. For example, you're offering mini-sessions that are 15-minutes and you want a buffer of 5-minutes in between each session. You would need to set up your Date Length to be 15-minutes and your increments to be 20-minutes (i.e there's a slot available every 20-minutes). You would also set your buffer after your events to 5-minutes.