I been working out for over 1 year but not to gain weight, actually the other way around. I started at 160lbs (I'm 5'6) and now I'm at 142lbs with a lot of lean muscle. I do a lot of cardio and I don't do too many heavy weights. In a few months I might consider gaining a few pounds in muscle but for the mean time I want to get cut.

If you want to gain muscle weight you have to eat A LOT of protein. Your biggest challenge will be at your kitchen not the gym.