To gain muscle mass I suggest you focus your time on compound exercise like squat, deadlift, bench press, dips, pullup, stiif leg deadlift and clean and jerk.
These exercises are excellent to stimulate natural human growth hormone and testosterone in your body. Make sure to train to failure with 6 to 8 reps, do no more than 2 sets to failure. Train no more than 3 times per week.
In order for your muscle to grow they need rest, so make sure to sleep a minimum of 8 hours per night. Eat 1.5 to 2 grams of protein per pounds. Eat enough calories ( multiply your bodyweight by 17 at least... so if you are 200 lbs multiply by 17=3400 that's the minimum)
Drink lots of water like 8 to 10 glasses a day minimum(Muscle are made up of 66% water)
Simple formula for muscle building: train hard, eat lots of protein rich food with enough calories and rest, rest, rest.
Hope it helps
