Okay so I want to be an actress. This isn't one of those stupid dream things everyone has. I have no experience in acting, but I love to act around family and friends. And honestly, I think I'm pretty good at it. I want to take an acting class, but I'm scared people would laugh at me since I have no experience. Im 15 years old-help please.

You should go for it! It sounds like you've got a natural talent for it, and you obviously have the desire. Acting classes get new people all the time, so they'll be used to inexperienced people. Sure, you may find other people your age who've already had years of experience, but you'll also find lots of people your age and older with no experience at all. There'll probably be plenty of "newbies" in your class, but even if there aren't, you'll only be the "new girl" for a short time. Break a leg!

You can't be an actress if you are scared of what people think. The whole idea of acting is convincing your audience of a persona and emotion. When you act, YOU are setting the tone, the mood, and THEY are swept up in what you are.
So - stop being scared.
If the instructor is tough, all the better for preparing you for your career, where no one will coddle you, and you might get yelled at, all part of the job.

If that doesn't work for me, I am also really interested in being a model. I have braces right now, so I think I'll wait until I get them off. How should I tell my parents I'm interested in modeling?

For what it's worth, an acting career can last your entire life. A modeling career, on the other hand, very, very, very rarely lasts beyond your mid 20's. That may seem like a long way away now, but in the grand scheme of things it's nothing.

Nevertheless, you should chase your dreams while you can. If you have your heart set on modeling, don't let anybody stop you.