You could be banned for multiple reasons. If you're banned for 24 hours, it's likely that you said something inappropriate, which is against Club Penguin's guidelines. If you're banned for 72 hours, it's likely that you used a third-party program (Such as Penguin Storm or a Trainer of some sort) to cheat or hack the game. If it's forever, then it means you've broken the rules too many times. You can ask Club Penguin to unban you, but you have to include a good reason and promise not to break them again, or they won't unban you the second time.