Controller Buttons
The B-Button is a Button featured on all console controllers and all hand helds. This button on most consoles is used to swing's Link's sword (all other than the Great Fairy's Sword). In Ocarina of Time you can change which sword you use with your B-Button.
C Button
There are 4 C-Buttons on the Nintendo 64 controller. Up, Down, Left, Right. In the Nintendo-64 games the Up C-Button is used to talk to your Fairy (Navi or Tatl). The other three are to use item which you equip on to them.