How does a body travel in outer space from one point to another?

Larger bodies, like planets, just coast from place to place, having nothing to slow them down. Space ships, on the other hand, propel themselves forward by pushing stuff out the back. These guy's physics is true and all, but the best way to put it is with commonplace objects. Take a gun. You shoot, the bullet flies out, but you get pushed back. That's /EXACTLY/ what happens in a rocket.