Anenomes are carnivorous, they sting and kill small fish, crustacea etc. The Clown Fish secretes a slime which confuses the receptors on the anenome it lives in thus receiving protection from the anenome. It is thought that the anenome also receives tidbits from the clown fish so it's not a one way thing.
Traditionally you feed anenomes with bits of shrimp or prawn, but they'll eat most things.
You'll get a better answer from a marine keeper.