Events from your Calendar will be displayed as options for the drop-down list of the form that has been set. This step helps you set up the format so that events can be distinguished from each other so that your customers can easily identify them to choose from. You can study more formats in many languages here
Google Forms is great and free. Google Calendar is great and free too. Our work is sync the Calendar with "drop-down" field of Forms. You can set up the Appointment Scheduling System for your business in 5 minutes. It just cost $1/1000 bookings.