There are 2 ways to make service bookings, depending on the device you are using (Desktop or mobile) one will work better than the other.
On desktop the easiest way to make service bookings is straight from the calendar, in the sidebar click on Calendar, navigate to the day you wish to book at and click and drag with your mouse the period you want to reserve.
On mobile, the easiest way is to use the Add service booking link in the sidebar.
Depending on the strategy you chose, you will have a different visualisation, but the fields to fill in will be the same.
You will need to select the pet type, then you can create or select an existing customer.
Once you have a customer selected, you can choose the pet.
Finally you will need to select the service you want to book.
Based on the configuration of the service type, you might need to set a price.