You can buy a map that has all the bus routes on it. The fare depends on how far you go. Tell the seller where you're going, and she'll tell you the fare. Taxi cabs are more common in China now, and they're generally cheap, although you won't be able to afford to ride them daily on your Chinese salary. The bone-jarring yellow mian di taxis are particularly cheap, but will be banned in Beijing after 1999.
Minibuses are also common in bigger cities.
A ticket taker yells the bus's destination out the window and stops to pick up anyone interested in riding.