MY WEIGHT IS 40 KG AND WANT TO PUT ON WEIGHT

For weight gaining simple start doing some exercise. Eat some healthy things like bowled eggs, milk, meat, salad, fruits, juice. With exercise you can take some whey protein but some good brand. Do these all on regular basis.

I totally agree with you. Eat more fatty foods and junk foods like chicken and burger and also drink protein shakes to gain weight. But don't forget to do exercise because if you will eat more junk foods for gain weight  then you may gain overweight so do exercise cause it will help you to maintain your weight.