The speakers in my car aren't working?

ok i just got a new 1991 Honda prelude and it has after market speakers in it and there's two tweeters up from but when i play a CD the tweeters work but the same sound comes out of the back speakers to and there is also one amp in the back of the car that has two plugs just laying there but there's no place for those to be plugged into pleaz help i really want my music