The best way to become an actor is to “act.” While classes help, they are not a substitute for actually getting on the stage or in front of a camera and acting.
Look around and find a local community theater company that is doing a play that interest you, and audition. There is where 99% of the people who are actors get their start. Learn from the others around. Do NOT limit your involvement to just being the stage. Help out the make up person, do some costuming, help to put up a set, dress the set, volunteer to assist the director. That way you will understand how to have your make up done, or how to block a scene so you will know how to move on stage, what the wear, etc. All skills that will help you if you do continue in acting.
If you find you like it, have any kind of a talent, and can tolerant all the egos, nonsense and competition that goes on behind the stage, then it is time to thing about classes. If money is any issue, most colleges (including local community ones) and many larger high schools have theater classes and/or a theater group. Take advantage of them as they are cheaper then “acting only” classes, and you can get grants, scholarships, loans, etc.
Watching YouTube videos will help. But it does not take the place of actually being on the stage (or in front of the camera.)