Resource (as it is used thru out this discussion with the templates) is a valuable resource or commodity that you wish to schedule or measure or display.

Schedule and Bookings.

Therefore a Resource can be an Employee, Doctor, Dentist, Mechanic, Service Bay, Item for Rental, Apartments, production machines, etc.

The templates will run against your existing files if they have a key with unique identifier for the resource.

TimeLineDD is a powerful display mechanism for displaying resources.

Resource can be any of the above, with measuring their appointments(time) 

products and sales counts, totals, and or averages per time period

invoices display counts, totals, and or averages sales per time period

embed points provided to manipulate the data as you may need, loop thru child files, etc.

Customer (display field in Schedulers) is scheduled against the Resource.  This field should not be left blank, and can be many things.  Another employee, a customer, Lunch, Vacation, meetings, etc.