Every professional casino player who is now an expert has started somewhere and then kept building up their skills. Everyone used to be taught by someone else. Self-taught professional players do not exist.
You too need to start somewhere. When you’re interested in a game you have to know its rules, and they are provided by someone else. Unless you’re the creator of the game, you need to get at least some information about it from an outside source.
There are online materials that can help you become a professional player. But the easiest way to do that is to be taught by a professional player. Many professionals are defeated by their own students later down the line. You get to adapt their style of playing and observe their weaknesses, which eventually lets you defeat them.
Learning from a professional has to include playing the game a lot, because that’s what they themselves did too. You also need be consistent with your strategies once you pick them.
Online forums are a good source of information about gambling too. You get multiple opinions and strategies, you can choose the ones that suit you the best.
As long as you are willing to keep practicing daily for a long time, becoming a professional casino player is not complicated. You also need to remember that in order to succeed you need to fail first.