We all have different body types. So it all depends on many things. But from what i'm seeing in your pics, you would have to increase your protein intake. If you don't eat meat it's fine. You can get it from greek yogurt, pumpkin seeds, boiles eggs, quinoa, almonds, lentils, brocoli etc. Avocados are also good as they give you good fat. Going to the gym is a plus!
RE: To Gain Weight