Are you involved in local community or school theater? That's a great way to start auditioning and get good experience acting. There may also be some local casting agencies in the Pittsburgh area that cast TV and movies in your area - but you'll probably need an adult guardian to help you with that until you're 18. Maybe you could talk to your parents, or another adult you're close to, about your interest in researching/reaching out to local casting agencies?
If you spend the next few years doing theater in your area, and pursuing local acting opportunities near you, when you're 18 you can decide if you're ready to move to a city like New York or LA (where there are the most acting opportunities), to pursue it professionally.
When you see teenage actors in TV and movies, they've often moved to one of those two cities with their families because the whole family is committed to starting their acting career early. But many young people like you pursue theater and opportunities in their hometowns, decide whether or not they want to study performing arts in college, and then make the move to professional actor when they're a little older.