Your availability on your Scheduler is where you're going to choose when your clients can book a time slot. You can simply click on a date, add the available time window, and click "Add New" to add it. You can specify whether you want it to appear for:
This date only
All of a certain day of the week (All Fridays for example)
Specify certain days of the week, which lets you apply that same time frame to multiple days.
On top of choosing the time slot, you can specify the minimum amount of notice you need before scheduling a time, the timezone, and the time frame they can book within. Your options for the time frame are:
Rolling Window, which lets your clients book in the next X amount of days/weeks.
Start/End, which lets them book between 2 specific days.
Ongoing, which means there isn't a limit on when they can book.
Advanced Availability is where you're going to fine-tune the details of the date. This is where you're going to say how long the time slots can be, who can book them, etc. The available tools are:
Scheduler Type, which is whether 1 person can book a time slot, or multiple people can (for something like a workshop).
Availability Increments, which is where you set the frequency and granularity of available time slots for your invitees to choose from. Note that this is different than the length of the date.
Buffer After Events, which is how much time you need after an event.
Users, which is where you'd add additional users to the Scheduler. Your client can choose who they're booking a time slot with this way.
Maximum Available Per Day, which is how many events you want to book in one day.
Buffer Before Events, which is how much time you need before an event.