Im Almost 18 Years Old And I Weigh 42 Kgs.

Im almost 18 years old and i weigh 42 kgs. Im 5.26 ft tall. I want to gain weight. My eating habits are fine but i do not gain weight. My metabolism is fast. What do i do in order to gain weight? Should i use any supplements or not? And if yes then which supplements should i consume please name them..