Igneous rocks form when magma cools and solidifies, either underground (intrusive) or on the surface (extrusive). Metamorphic rocks form from sedimentary, igneous, or other metamorphic rocks undergoing changes from heat and pressure. Sedimentary rocks form from compression of sediments such as small rocks and organic matter. Rocks come in three main types - sedimentary, igneous, and metamorphic - and should not be thrown at animals or people as they can cause harm.