Be sure to have your parent's help you with anything you apply for--you don't want to accidentally send your information to a spammer!
Until Twitter finds a consistent way to weed out spam accounts, you will probably be followed by some random person who turns out to be a spammer.
What happens after you follow a spammer is that they bombard your Twitter account with spam-tweets that are similar to ones that you get in your email.
To tell if you have a spammer following you, a good rule of thumb is to click on their profile and see how much information they have available.
If you don't use your MySpace account frequently don't leave it there for a spammer.