An axe is a tool used to chop or cut things like wood. It has a long handle with a sharp, metal head at the end. The head is usually shaped like a wedge with a flat side and a curved side. When you swing the axe, the sharp side hits what you're trying to chop and splits it apart.
Think of it like a big toy hammer that grown-ups use to break things apart, but instead of hitting a nail, it is hitting a piece of wood to make it smaller. It's also important to be really careful when using an axe because it's very sharp and can hurt you if you're not careful.