Dentists see really bad teeth all the time; it's their job. They also don't want to hurt you, but understand that there are some procedures that can sometimes hurt, particularly if you haven't been in years (or never). Ask questions about anything that concerns or confuses you, or that you're curious about.
For a first visit, they most likely will not give you braces. Why not? Because that requires a bit of work on their parts, plus braces are somewhat costly and they may need to work with your parents on a payment plan. More likely, they will give you xrays. They'll put a heavy blanket over your body and then ask you to bite down on something, which has the film in it. They will then flip a switch and you usually hear a faint buzzing sound. Then they'll take the thing out of your mouth and put another one in, reposition the xray machine and do it a few more times, in order to get a picture of all of your teeth.
It's highly likely that they will also look inside your mouth. Usually this is done with a metal tool that is narrower than a pencil but has a mirror on the end of it that's maybe the circumference of a nickel. They will ask you to open your mouth wide and will look around.
It's possible that they'll also clean your teeth. Cleaning involves them using scrapers to get the more stubborn stuff off, and jets of water to rinse the food particles away, and they will give you water or mouth wash to spit out if your mouth gets full with the water or they just want to clear the surface. They will brush your teeth and floss them, too.
They may give you some education in how to care for your teeth, and might give you samples of toothpaste and floss, and even a new toothbrush.
PS My dentist is kinda cute, so I always like to see him, and the hygienists are always so nice. A lot of dentist's offices are like that, that is, they are friendly people like you and me, doing their jobs and trying to make you as comfortable, reassured, and healthy as possible. But the attractiveness of your dentist may vary.