When should i start saving money?

ive been interested in 401k and the stock market for a wile now. ill be working full time until august, and then i'm going to school. what i want to do is retire at 40. should i start investing now or should i wait till im out of school when i have enough startup capitol to actually make some money? i need advice. i dont really know much about either the market or 401k but im willing to learn.