The Need for Wii Memory
Without a memory card or some other way of saving progress, players would have to start their games over again every time they started up their Nintendo Wii. Memory options let you play games over longer periods of time without starting over.
Internal Memory
The Nintendo Wii comes with built-in memory. That means that for most purposes, you won't need to buy a separate memory card. When playing a game, your progress will save right to the console.
SD Card for Portable Memory
If you want to bring your game to a friend's house, you can use an SD memory card to save your progress.
GameCube Memory Cards
Since GameCube games can be played on the Nintendo Wii, you'll need memory to save your games. GameCube games can't be saved with the Nintendo Wii internal memory, so you'll need an original GameCube memory card. It fits in a slot on the top of the Wii.
Extra Storage
The internal memory on the Wii is 512MB which is enough for most uses. With lots of WiiWare or Virtual Console purchases, that memory can shrink fast. SD cards are good for freeing up memory on the console.