Only really once igneous rocks have been eroded and then redeposited by water or wind do they become sedimentary. Rocks that change - such as sedimentary rocks that are transformed by heat and pressure - are generally known as metamorphic rocks.
Sedimentary rocks are formed by depositied layers of sediment, usually at the bottom of a lake or sea. Over time the sediment layers are compressed and heated and sedimentary rock is formed.