Hi friends, I am 6 ft tall but i am very thin only 55 kilos. Please let me know how to gain weight. Help me?

i dont have time to go gym. Even though i am very thin , i am healthy..what i have to do to increase my weight, any medicine or any health drink. And i am poor eater, i eat very less n choosy...i cann't avoid it. so i have left with no ohter option than going for this health drink or medicine. I have heard about endura m ..is it worht n safe...please friends let me know...thank you