Having worms in your tummy is not very nice. They can feel wriggly and itchy, and can make you ill if you have them for a long time. You can get rid of them by going to the Doctor for some medicine, but the best thing to do, is avoid catching them in the first place.
The most common kind of worm that people can get living inside them is called the "Threadworm". They are small little white coloured worms that are about as long as your fingernail. They can sometimes be called "Pinworm", but their real name is "Enterobius Vermicularis". That's a long name for such a small thing!