Chapter 3 of the Getis Textbook briefly discusses the three types of rocks that form the Earth’s crust. While it mentions the rock cycle, it does not do it justice in terms of explaining its importance in linking the three types of rocks.
This page provides some great information and animations that better describe the rock cycle and its importance in shaping the Earth’s physical landscape.
Essentially, the rock cycle is the theory that all minerals on the Earth cycle through the three forms of rock over the course of millions of years. That is, igneous rock first forms from magma that rises from the Earth’s mantle. It eventually erodes and is carried away as silt, sand, and gravel, which eventually settle in a body of water where it becomes sedimentary rock. As the tectonic plates shift or magma collects within the Earth’s crust, heat and pressure cause igneous and sedimentary rocks to undergo physical and chemical changes at the molecular level, creating metamorphic rocks.