They are not that sort of garage!
Here is where the confusion has arisen.
These type of cycle carrier use the towbar or towball.
Racks will either clamp around the towball itself, meaning that you cannot tow at the same time as using the rack, or they bolt to the towbars towplate, leaving the ball free for towing.
This latter type is only suitable for old style bolt on towballs and cannot be used with swan-neck or euro type fixed or detachable towbars.
The racks then either have a pair of arms (or in some cases a single arm) onto which the bikes are hung OR they are platform style and the bikes sit onto the rack.
Most towball cycle carriers are suitable for 2 bikes, some are suitable for three bikes and there are a small number of this style of rack which can carry 4 bikes.
Some better quality racks will have lighting built in to replicate your vehicle lights should they be obscured.