This feature is available only with a work or school Google Calendar account.
You can set up a block of appointments on your calendar that other people can reserve. For example, professors can invite their students to reserve time during office hours each week.
Appointment slots are useful when you don’t know who needs to meet with you, but you want to make yourself available. You can offer people a block of time on your calendar that they can book time slots within. For example, you can set aside 2 hours that you’re available to meet with people in 30-minute slots. Others can then book one of the 30-minute slots within that time that works best for them.
Set up & share appointment slots
How appointment slots relate to regular events
When you create a block of appointment slots, the block shows up as a single event on your calendar.