The C-Gear allows you to use certain features of wireless and wi-fi communications wherever you are. It is on the bottom screan of the DS and has three buttons that can be touched to use. The buttons are IR, Wireless, and Online. IR allows you to Battle, Trade, exchange friend codes and check the feelings of your Pokémon. Wireless allows you to go to the Entralink or use the Xtransceiver to talk to other people. Online allows you to send one of your Pokémon to the dream world.
From StrategyWiki, the video game walkthrough and strategy guide wiki