Resources can be booked for appointments to ensure that a resource is not double booked.
You can create and edit resources via the settings which are explained here: Resources settings
To see available resources you'll need to access the Calendar module and click on the Resources menu and then Overview.
Here you'll get a GANTT-view of the different resources created in your solution and see what resources are booked and available.
To book a resource simply follow this guide: Create a calendar appointment