Your abdomen (or abs) is important to you. It is a big muscle that contains your stomach, liver and intestines, your kidneys and bladder, and your reproductive organs, and helps to protect them all. Keeping it in good shape can help you to look toned (its a good way to get a six-pack, in other words), and also to feel better in yourself.
Luckily, ab exercises are easy to do. The most popular is probably the ab crunch, which is when you lie flat on the floor, bend your legs and then touch your knees with your elbows. You can also try the simpler sit-up, which is the same thing, only putting your head between your knees each time instead. Which one you find easier will depend on your body but its probably better for you if you practice whichever one you find the most difficult! This way you will tone-up your less-used muscles instead of focusing on ones that are already just fine.
You can also get various machines and gadgets that will help you in your ab exercises the number is increasing every day, in fact. Some of these are good, while others are just expensive rubbish. As a rule, dont buy anything that you havent tried out for yourself which means that you cant get that special deal from the shopping channel, unfortunately. Go to a shop and insist that you need to try out a few different ones before you make your decision, and if they refuse, just leave.
One last thing: it is important to realise that ab exercises are no good at all for losing weight. What you are doing is building muscle, not so much burning fat although some fat is burned, the effect is negligible, and ab exercises certainly have no special effect on an overweight stomach.