Gain muscle. If you have an Ectomorph body type, you will need to work very hard and consistently in the gym to get results. I worked in a gym and was extremely impressed by one really skinny, ectomorphic guy who came in religiously, by himself, and worked at weight training. He achieved a very toned and sinewy muscular build. It was very inspirational to see. And he proved that it can be done. You can change your body type.
Protein powder helps, along with a healthy diet of many small meals (or snacks). You don't want to eat fatty foods because you'll keep skinny limbs and get a fat tummy. That won't look right.
If you want to gain weight, focus on hefty foods like potatoes, corns, dense breads, cream soups and protein shakes. Drink a lot of water since being hydrated is very significant for your body, particularly as your body is experiencing changes. Add pistachios or roasted channa to your diet and make them your evening snacks.