A crossbow is a special kind of bow that is held upright like a gun. It shoots arrows, which are also called bolts. Crossbows have a special mechanism that helps you pull back the string really tightly, so when you let go, the arrow goes really far and really fast. It's like a really powerful toy gun that shoots arrows instead of bullets. But it's not a toy - it's a very dangerous weapon that you should only use under the supervision of an adult.