I'm pretty thin (138 lbs.) and I'm 21 years old, and the main reason for this is that I'm an ectomorph (my body type is naturally thin and I have a fast metabolism). I am not able to eat six meals a day of eggs and steaks and rice and everything I'd like to do, but I can get peanut butter and jelly sandwiches, protein shakes, and simple stuff like that. I just don't usually have time or access to cook meals or anything.
My question is: what's the best way for someone in my situation to get muscular? What are the best simple foods to eat as far as protein is concerned, and what are the best exercises to build muscle overall? How many protein shakes a day should I drink? Any linkage or suggestions would be helpful, thanks!