How do you become an artist? Being an artist is a job OR a way to communicate. Or BOTH. Here I talk about the "both" part.
As a child, you fastly learn something about art and artists. By chance, while your identity takes shape, you can decide that you want to be like them, like the artists (or also to become an explorer, or an astronaut, or have other models). Growing up, you can see that trying to paint, or to sculpt, or to draw, is something that you like. Your brain seems to manage pretty well that way, seems to work easily in that norm. But can you do that for a living? Well, a lot of people do that, and they make good money, as far as you know.
So you make your choice, even if actually you don't know if you can walk that path. It's a challenge.
You keep working on your "art", and try also to discover the way to sell it. You may have to find a job, becouse your artworks don't let you earn much, for now. So you stay with uncertainty about your ability as an artist. How long? A lot. It can last a lifetime.
Mind you, having doubts about your own art is not a bad thing. If you have no doubt, and you are sure to be a great artist, that is surely worse than continuing to doubt. But having doubts about your art is one thing, not knowing if you actually can be an artist for a living is another.
The fact is that trying to be an artist works that way: it takes decades just to understand if you are actually able to do it. Unless you are very lucky or incredibly talented.
Above, my artwork "The only flight", 1994