First you need to act. A lot.--as much as you can while you are in High School at school and in the community.
Do not get in a hurry, it takes a lifetime to become an actor.
Watch out for scams. The scammers prey on the over eager.
Learn about the business of acting. It is just like going into any other business; it takes money, experience and a good product which is you as an actor. It must be promoted properly to be a success.
What you see on the tv and film screen is not the acting, that is not what the actors do all day. Mostly they sit around and wait, Film acting is not that exciting. Everything is rehearsed and done over and over until it is right, then a small clip of it is edited into the film with sound and music to create the illusion that these things are happening to the characters.
Learn to be humble. The business does not like strong egos.
Experience is more important than training.
People who succeed are not necesarily the best actors, they may be the best self promoters, or the best personalities, but they must have enough talent to do the job or they wouldn't get it.
Don't try to do anything professional while in High School, plan to start working on being a professinal after you graduate, unless your parents make something happen for you.
Until you are 18 you cannot sign a contract or do anything professional without one of your parents being there. Your parent has to get you an agent if you are to have one before you are 18,
Read and study my free book. Reread it and study it some more. Learn all that is in it and put it to use.
To really succeed at acting takes LUCK more than any other thing.