Answer:
Pencils are made out of wood and have a graphite filling which puts the mark on the paper. Pencils used to use lead but they found that it could be poisonous. This mark can be rubbed out, but may look scruffy. Pens are more formal but use any coloured ink, the ink is normally blue, black or red. Once this ink touches the paper it soaks in, making the mark permanent, so if you make a mistake, you have to use liquid paper (white out) to cover over it. Some pens have special erasers that can remove the ink. Hope I helped :P