I recently bought a receiver for the 1st time, and I'm just learning about Audio tech. The fisher floor speakers that I'll be using have 2 screws in the back of each one for connecting wire. Above one screw it says "8 Ohm" with an arrow pointing to the screw. Above the other screw it says "common" with arrow pointing to screw. What does "common" refer to? And, how do I connect these speakers? (there's also an RCA Plug connection).