Sir i m very thin i want to gain fat

the best way to gain weight is when you add 400-700 Kcal to your BMR, this addition should accompanying with weight training to gain muscles mass and get bulking body.
Meals should be eaten every 1 hour and thirty minutes to two hours. Keeping a constant flow of nutrients in the body is essential for gaining mass because if you have nothing to build muscle with then you won't go anywhere, you should be eati at least six meals a day to ensure he is getting enough nutrients for your body to grow.
These are something that will just help you get his calories in, supplement such as True mass, Serious mass and Pro gain can do, but pay attention, these thing's should be eaten in moderation because it will do the body more harm than good since they aren't nearly as good as real food, he shoud get his needs of protein, carbs and fat from natural food as a primary sources.