An event is a set of fixed time periods on a calendar.
The client simply selects one of them.
If there is only one slot, the system will choose it for the client.
Rental it's time on the calendar, divided into intervals.
The client selects the start and end point of the reservation separately.
In the rules for the operation of such a resource, you specify a set of such points that divide the time into intervals.
Try to book the various options for the work of resources: