Creating an Appointment Slot Calendar in Google Calendar
Create a new calendar (or use an existing one) and give it a name. Change the settings as appropriate for your needs.
Click on a slot on the calendar (when viewed in day or week view only) and choose appointment slots.
Click edit details and create a more detailed appointment slot type of calendar.
When you click on the link to fill in appointments, this is similar to the view you will see and how you register for the slots.