This is pretty obvious. It is about licking each others anus. This is not nasty if done correct. So first of all keep it clean and keep it trimmed. Do not try to push you tongue in all the way it is all about the outside of the anus. Eating ass or rimming your butt is slang for it. Overall most people love to receive it but are sceptic of giving it. But hey just try it one time and you will be addicted.