You cannot target body fat in one area of your body such as your tummy - you have to reduce your body fat percentage as a whole. Cutting calories and eating wisely will reduce your weight, while exercise and good nutrition will help you to maintain or even enhance your muscle mass and metabolism.
My advice on starting out exercise is that brisk walking is a great exercise in its own right. It is particularly suited for people who are starting out with a low level of fitness. As fitness increases, try walking at a brisk pace, up hills, and / or for further distance. Wearing a pedometer is a great help - you can use it to set goals, such as walking 10,000 steps per day etc. At some point, you might want to start trying some interval jogging, something that might develop into a regular jogging or sprinting practice. However, they are other forms of exercise - walking for medium to long distances is a fine way of getting fit.
Other forms of exercise you might want to experiment with as time goes by - cycling (both road and cross country), swimming, exercising at home to DVDs, aerobic, kick boxing, pilates, or yoga classes, gym membership, strength training, running/jogging - experiment, find out what you enjoy, and set yourself goals to achieve. Dont set yourself obstacles - give things a go! The secret to success is to carve yourself a new lifestyle.