You should definitely start at some local schooling shows! Find some relatively well-fitting show clothes (you’ll need a jacked, plain blue or black), and show shirt (LONG SLEEVES! If you show in the summer and it’s really hot, they only let you take your jacket off if your shirt has long sleeves!) with a collar (start with a plain color for the shirt, like a simple white or pale pastel), and a belt for your riding pants. If you are under 12 you should get johdpurs with the leather garters; get someone to show you how to wear those, but for hunters they are an absolute must. If you are any older than that you need breeches and tall boots. If you have tall boots, you need to put your hair in a hairnet (also get someone to show you how to do that, and keep that in mind for when you’re buying a helmet) but if you have johds then you can do two neat braids with nicely tied bows. Make sure you have a nice black show helmet, no plastic. IRH makes nice, inexpensive, beginner ones, but if you’re sure you want to show at a higher level then then invest in a Charles Owen.
Now, always show at least one level below what you ride in lessons; I’d even recommend two levels lower. It’s always good to start with easy hack (flat) classes. Another thing you can do is go with your barn or with a friend to a show but not compete, just be a groom or even just watch and observe the other riders. There is a lot of etiquette to be learned, especially like the schooling ring etiquette. Definitely DO NOT go to your first show without a trainer!
If you have any more questions, feel free to ask :) good luck <3