Chillin' is an American ghetto slang word that is essentially a cool way to say "I'm bored." It causes a great deal of confusion for exchange students learning English in the US. Here is a usage example:

G-Homey: Wassup dawg?
P-Phunk: Chillin'. Whatup wit' you?
G-Homey: Smokin' some weeeeeeeeed!

This form of speech is perfectly normal in most parts of the United States, thanks to cable television.