The rock cycle is a unending process that changes rocks from one to another. It could start anywhere from igneous rock, metamorphic rock, or sedimentary rock. Igneous could change into metamorphic or sedimentary. Metamorphic could change into sedimentary or igneous, and sedimentary could change into metamorphic or igneous.
Igneous rock is formed when magma cools and forms crystals. Igneous rock can either form on Earth's surface where the magma cools fast or underground where the magma cools slowly. Magma is in volcanoes, and when it erupts the magma turns into lava.
Metamorphic rock forms whenever heat and pressure is added to a rock. The rock "morphs" into something different. Metamorphic rock was either igneous or sedimentary at one time in the cycle. Two examples of meta"morph"ic rock are gniess and schist.
Sedimentary rocks form when layers of sediment are packed down with wind, water, dirt, soil, etc. over many years and are cemented together. This is a way igneous rock changes into sedimentary.