Physical activity does four things for me. First, it speeds up my metabolism so that I burn more calories; second, it suppresses my appetite; third, it increases my energy level, and fourth, it makes me feel good about myself and the way I look.
Exercise, depending on its intensity and how long it lasts, will elevate your metabolism anywhere between one and several hours after you have finished your workout. In other words, you will continue burning calories at a faster rate than normal after you have stopped working out. One of my goals over the past 11 years since my surgery has been to change my body composition by increasing my muscle mass and reducing body fat. I have accomplished this through strength training (weight lifting). Increased muscle mass increases your body's fat-to-muscle ratio which boosts the rate at which you burn calories all the time, not just after exercise.
In my case, exercise suppresses my appetite. I am just not as hungry as I am on the days I do not exercise. Plus, you have less time to eat if you are in the gym for two hours. I choose to exercise early in the morning for two reasons: I am never too busy at 4:30 in the morning and it jacks me up for the whole day. I feel great after exercising. Of course the exercise alone will not work if you don't employ a sound eating plan along with it.
I encourage you to see your doctor before starting an exercise program. Start slowly and get proper instruction on the use of the equipment to avoid injury. Let me know how physical activity affects you.