Sea anemones are closely related to coral and jellyfish. They eat small sea creatures and small fish that drift past them into their tentacles. The tentacles have poison in them, and the anemone stings them to kill them before it eats them.
Sea anemones spend most of their lives stuck to the same rock or other surface, but can unstick themselves and swim to a new rock if conditions aren't good for them, such as if their rock dries out for too long or something is trying to eat or damage the anemone.
Sea anemones can reproduce in the usual way by releasing eggs and sperm, but they can also reproduce by budding off new anemones or by splitting themselves in half to form a new anemone.