*Set "Quantity of This Type" to the number of rooms of this room type.
*Enter the number of Guests
*Set "Requires Availability in" for each of your real rooms. The order defines where bookings will be placed first.*Set "Combination Logic" to "Any Room must be available"
*Set "Assign Bookings to" to "First Available Dependency Room"
*Leave all other settings on the defaults.
To assign a booking to a different room just open the booking and change "Unit".