First we have to look at the rocks inside the Earth. Igneous rocks are rocks that were once molten. You can usually find those around volcanoes.
Sedimentary rocks are because lots of minerals and other rocks have piled up.
The basic idea is that there are 8 major and a whole bunch of minor plates on the surface of the Earth. The plates are like the skin of the planet, constantly moving around the planet. When we say constantly moving, we're talking centimeters each year. You couldn't sit down and watch it happen. You could if you watched an earthquake.