They are basically the same card that expands the memory of a cell phone. You have an adapter that plugs into your computer. This card then shows on your computer as another drive. You simply copy games over to this card. Please note: the games you copy are not usually a licensed copy.
You then place this card into the other adapter that fits your game.
Pros: Very simple to use, can store lots and lots of games, inexpensive.
Cons: Games may not be licensed ... i.e. you may be using an illegal copy. Some more modern games may not work (a very small number)
Ted