To add a booking directly to your calendar, go to your Appointedd calendar screen:
Click Add booking, or simply click the empty interval in the calendar
Select the service
Select a duration and resource (if applicable)
Select the date and time of the booking (note that bookings cannot be made for a time in the past)
If an existing customer, click Search existing customers... and type the customer's name to find and select them
If a new customer, click Create new customer
Click Add note + to add any notes to the booking for each customer
Click Create booking to add the booking to the calendar.
Here is a video taking you through the process
What to do if you cannot make a booking
If you're unable to make a booking, it will be because an aspect in the setup of your account prevents it. Can the resource selected perform that service? Is the time available in your custom schedule?
This troubleshooting guide will help you to identify what it preventing you from making the booking.