Exercise for Those Who Want to Gain Weight

Most of the time when we think of exercise, we think of losing weight. But that isn't always the case. There are several people who workout because they want to gain weight. Ideally, the weight gain would come from added muscle.

To put it simply, gaining (healthy) weight involves proper nutrition and a lot of heavy lifting.
Eating more before and after your workouts will help to feed/refuel your muscles, and lifting heavy weights (with good form) will help build up muscle mass.