O.K, say you on a train playing ping pong. As you and your opponent hit the ball back and forth the ball seems to be moving at the same speed it would be if you were playing in your home. But to a stationary outside observer the ball is moving as fast as the train. The speed of the ball is relative to the observer. For you it appears slow to the stationary observer it going un-naturaly fast for a ping pong ball. Anyway, if you were to even run from one end of the train to the other as fast as you could your still traveling at the same speed as the train. Hence if it were possible for anything with mass to travel at the speed of light ( witch it is not ) you could take as many steps forward as you would like but never go faster than the speed of light. Much more to it than that though. Ive got some really good books on the subject. If your interested in them let me know