There is no "nun chuck" built into the Wii Remote. You are likely thinking of two separate accessories:
An attachment that plugs into the bottom of the Wii Remote, adding a more precise gyroscope for enhanced motion tracking (required for games like Wii Sports Resort and The Legend of Zelda: Skyward Sword).
A separate, wired controller that connects to the Wii Remote's external extension port. It features:
Together, the Wii Remote and Nunchuk form the standard two-handed control scheme for many Wii games, enabling actions like aiming with the remote while moving with the stick.