
If you wish to gain weight, whether little or more, then Eating properly should be your priority. It is the best and foremost thing to do if you really need to put on weight and muscle.
Simple Fact: You must get more calories for your body than the amount of calories you burn.
But eating nonsense (Junk) will not help you, you need to eat more but at the same time you need to eat healthy. By doing this you will get some extra fats and calories for your body. For that you need to have nutritious and healthy food i.e. food which includes your weight gain diet which will help you gain mass, not bad fats.
Caution: Enhance your diet pattern gradually...