Hello. Hope you are fine. Thanks for your query. Joining a gym would be a good idea, since there will be a fixed schedule of exercise for you and you are more likely to follow a good schedule for your regular exercise. Also joining a gym has added advantage of the chance to do specific workouts to reduce belly and waist fat. Eat healthy. Include a lot of fresh fruits and vegetables in your diet and avoid fried and junk food items. Drink fruit juices. Walk for at least 30 minutes a day. All this will definitely help you to gain a good body shape and also make you very healthy and free of any diseases. Take care.