While starting off with an online course is essential to a successful day trading career, the next necessary step is to spend the time and effort to test your skills and ideas in a real-time environment. Theory is great, but nothing can prepare you for the act of actually buying and selling except the simulated environment of a paper trading account.
Paper trading will allow you to see how your ideas and skills actually play out when confronted by the nuance, complexity and stress of making live trading decisions.