It would be just like putting yourself in the game. Just no pain, that's all. You wouldn't think "Move my arm" - you would just move your arm and rather than moving your real arm, the device would take that message and send it into the game. The science behind it isn't really... Real, I guess. I mean, obviously. In fact, making it work that way would be incredibly difficult and dangerous, considering it would be based on intercepting nerves and somehow converting the messages sent with them into data. However, that's the fun of sci-fi, isn't it? XD