The document discusses the three main rock groups: igneous, sedimentary, and metamorphic. Igneous rocks form from cooling magma, either underground (intrusive) or above ground (extrusive). Sedimentary rocks form through the compaction and cementation of sediments. Metamorphic rocks are formed from existing rocks undergoing heat and pressure without melting. The rock cycle diagram shows how rocks continuously change between these three types through various geologic processes.