You need to work up to 30-60 mins per day of aerobic
exercise at 80-85% of your target heart rate (220-age)
x .80 to lose weight. The more you do, the more you lose but this is the threshold for you cardiac health. Take it slow and work up to a steady routine. Don't over do it at first as it will make it less enjoyable and less likely to become a habit. Whatever you do, get your doctor's approval first.
Also, get your diet under control, no empty carbs like sugars, breads and pastas.