A basic controller keyboard will make no sounds of its own, but can be connected via midi to other keyboards and use the sounds from the connected board. Or could be connected to a PC via midi cables or USB (if supported).
Well what’s the point of this?
There could be various reasons:
Controller keyboards are available with 25, 49, 61, 76 or 88 keys weighted or semi-
Most keyboards that have their own sounds are also capable of additionally being ‘controllers’ via midi or USB. Some have better controlling facilities than others -