Room Type is a collection of rooms with the same properties, and under the same address (Example: Standard, Double, Family, Villa Blue).
List of rooms contains all the physical rooms in your property
Example: Room 101 is a "Deluxe" room type which has some amenities that differentiate it from other rooms 102 and 103 which are under “Standard” room type. So your property has 3 rooms, but only 2 room types.
Please note that in order to manage your "List of Rooms" you must first create the room types, and then add rooms and assign each room to the corresponding room type.