You need to eat calorie-rich foods that pack in the energy. Nuts, fats, meats, desserts, dairy are calorie-rich foods. You are more likely to gain weight if you plenty of these foods. It takes 3500 to add one pound of weight. So, if you have a target to gain one pound every week then you need up your calorie intake by 3500 calories in addition to what is needed for metabolic needs.
How do you calculate BMR(Basal Metabolic Rate)?
There is simple formula to calculate Resting Metabolic Rate(RMR) which is dependent on your age, height, weight and gender.