1) Igneous Rock
This is when lots of rocks ate heated to such a high temperature that they melt and mix. When they cool, they have formed a very different type of rock.
2) Sedimentary Rocks
This is when layers of dust, sand, decaying plants, bones and clay settle in layers one on top of another. They are then sandwiched together.
3) Metamorphic Rock
This happens in 2 ways. Fist it is when Sedimentary is put under a lot of pressure squashing it.