Wii Remote
Almost all Wii games depict the Wii remote -- the main controller for the console -- on the back of the packaging. This depiction is accompanied by a number. The number, which will be between one and four, represents the number of players that can play the game at one time. Each player must use a Wii remote that is individually synchronized with the console.
Nunchuk
The nunchuk, a rounded, smaller controller with a long cord, connects to the Wii remote to add additional controls to some games. Games that have a depiction of a nunchuk on the back require the use of this peripheral. For multiplayer games, you'll need to use multiple nunchuks -- you must have a nunchuk for each controller that is used. Games such as "Super Mario Galaxy" and "Wii Sports" make use of this peripheral.
GameCube Controller/Classic Controller
Game cases that depict the GameCube controller on the back also usually depict the classic controller. The classic controller is sold as a Wii accessory and is designed like the older Super Nintendo controller. It plugs into the Wii remote, while the GameCube controller plugs directly into the Wii. Games such as "Super Smash Bros. Brawl" and "GoldenEye" let you play with these controllers.
Other Accessories
Some games allow the use of more specialized Wii accessories. The balance board symbol that's found on some game cases calls for players to stand on this peripheral to control the action. Balance boards can be used for exercise titles such as "Wii Fit" and for sports games. A steering wheel symbol means you can attach your Wii remote to the steering wheel to drive your vehicle in some racing games, including "Mario Kart." The depiction of the Wii zapper means you can insert your Wii remote into the zapper accessory for better aiming in games that allow you to shoot weapons, such as "Link's Crossbow Training."