First of all begin to exercise regularly, at least 4 times a week if you don t have time. Do weight lifting with a certain program that I can send you an example if you want. You should eat proteins: white eggs, cottage cheese, cheese, milk , yogurt , chicken, fish and also a lot of salad and vegetable. You should take 0,8 g/kg protein per day. You should eat less fat and carbohydrates such as white bread, rice, spaghetti, cookies. Protein is important for building muscle.