One thing that we often hear at the club is that you want to gain muscle mass.
So what is the process to do that? It is best to understand that our body is only going to develop only enough muscle to deal with the current loads that you place on it. The more the regular, large load you move, the larger you will be become in relation to what your body needs. So the basic science of it: hypertrophy and hyperplasia. Hypertrophy is an increase in the size of the muscle due to an increase in the size of the muscle fibers, while hyperplasia is an increase in the number of muscle fibers. Not that we want to get to technical. But we can use this information to understand growth of muscles when you are working out. For example: if you want to gain strength without gaining much weight we would want to do single set with 10-14 reps, but if you want to get larger muscles and gain weight you should do sets of three or six with 8-10 reps with minimal rest between sets at the most amount of weight that you can handle for the duration of the sets. So with the goal of gaining mass or size, would involve repeating weights and creating stress on the muscles that we are working out. Of course more is involved than we could cover in a short blurb, such as diet, and other factors that can also lead you to your goal but this will get you going in the right direction.