This question already has an answer here:
Long ago I was watching a scientific video about light speed. At one point, the person said to imagine the following scenario:
You are on a train going from the Solar System to the Alpha Centauri system. The supposed train is going at almost light speed, and you are on top of it. While you are on top of the train, you move forward one step in the direction in which the train is moving. Are you going faster than light speed?
The guy in the video said that the answer is no. When I watched the video I had no idea what the explanation meant because I wasn't into physics at all.
I also can't find the video, but I am curious as to why a scenario like this would be not possible (excluding the limitations of technology, and other flaws in the scenario which have nothing to do with speed.) So, why isn't this possible? :)