1. From your calendar , edit the filters on the left hand side to show non booked facilities.
2. The calendar will now populate the available time-slots for your selected facilities.
3. Click on the desired time-slot and click "New Booking" in the top right corner.
NB - Only one client can booked be booked into a facility slot.
Be sure to check you have Facility bookings enabled.
You can find this in Settings under the Booking tab.