Instructions
Remove the cover on the back of the Wii Remote. Insert some fresh batteries (if they are not already). Locate the "Sync" button under the battery compartment. Keep the cover off.
Turn the Nintendo Wii on. Open the SD card slot and find the "Sync" button.
Press the "Sync" button on the Wii.
Press the "Sync" button on the Wii Remote. When the lights on the front of the remote stabilize, this will indicate that the controller has been synced. Put the cover back on the Wii Remote.
Use the additional controllers in any application or game that has support for more than 1 person.