It is fun to learn about coral reefs. This graphic shows how a reef is made. It starts as a fringing reef, then it is called a barrier reef, and finally it becomes an atoll.
Tiny animals build rocky cups for their homes with minerals in the sea. When they die, a new polyp builds on top of the old cups and a huge reef is made. This takes many, many years.
Coral animals are animals with stinging cells in their tentacles to catch prey. They are like jellyfish and sea anemones.