After you complete a small task for Fennel in Striaton City he will give you your own little C-Gear, which takes up the bottom of your two DS screens. The bottom-right three buttons allow you to change the settings, receive help and turn off and C-Gear completely (afterall, if you have no friends you might as well save your battery). However, it's the three main options, all allowing you to communicate with your friends, that we're now going to briefly look at.

These options all require you to be physically in close proximity to your friend, since they interact using the infrared signals between your game carts.

Battle: Starts an immediate battle between you and your friend, using the Pokémon you both have in your current parties.
Trade: Starts an immediate trading session between you and your friend. Allows you to trade from both your party and your boxes.
FC Swap: Exchanges Friend Codes between you and your friend.
Feeling Check: A compatibility checker between you and your friend. High levels of compatibility will be rewarded with one or two Sweet Heart.

Only one option is available here!

Game Sync: Syncs your game with the Pokémon Global Link.

Main Page: Coming soon!

Just the two options here, but also the two you are most likely to use!

Xtransceiver: Opens the Xtransceiver, allowing you to have a 4-way chat with your friends.
Entralink: Transports you to the Entralink Forest.

Main Page: Coming soon!

By tapping the C-Gear logo located at the top of the screen, you can customise the C-Gear to look exactly how you want it to. Initially just changing the shapes which appear on the C-Gear screen, it will soon be possible to download entirely new skins for the C-Gear via Nintendo Wi-Fi, allowing you to make your own C-Gear look unique amongst your friends!