Hello there! i'm 21 years old. my height is 6'1". on the other hand my weight is just 58 kilograms. how can i increase my weight & waist size. i need some suggestion like what kinda food i've to eat & what kinda exercise will help me?

Any balanced nutritional intake is good & can add calories but you likely prefer to add muscle mass to fat. All exercise routines should include a cardio component like jogging, fast walking, biking, etc. for 30 min/d. These will help stamina and increase appetite. You add muscle mass by using them. Free weights, machines, isometrics or other muscle stressors can help add muscle mass.

Agree with Dr. Ferguson. Do not overeat to add fat to your body. Have a healthy diet- http://www.choosemyplate.gov/. Wish you good health!