why bother? You aren't responsible for teaching your kids absolutely everything.
If you're talking about real swearing the words don't "mean" anything except "ouch" or "you idiot". If you're talking about slang terms for body parts etc, you could tell them, but why not just teach them how to use a dictionary?
If you're uncomfortable with them using such words around home (I was) just tell them not to do so. But they'll mostly pick up the meanings, and the propriety of using them, outside the home.