How do you gain weight by lifting weights?

Answer 1

To gain lean weight a person will want to eat more high calorie dense foods and eat every two to three hours. A few high calorie dense foods are peanut butter, lean red meat, bagels oats and dried fruit.

Answer 2

Exactly as you said: by lifting weights. Regardless of what type of weight-lifting program you are following, lifting weights will (and should; if not, increase the weight/reps) will increase muscle size and ultimately lead to a heavier weight.