What happens when you smoke weed, does it effect you?

Yes it affects you: The smoke itself from marijuana is probably less harmful than cigarettes, but it can cause paranoia in some people who are susceptible to it. And more importantly chronic marijuana use can dramatically decrease motivation, increase appetite, and lead to significant weight gain. There is pretty good evidence it can help some people with severe chronic pain and weight loss.

Yes: It can decrease motivation and your reaction time. It can be dangerous when driving. It can decrease brain volume.