I'm worried about my career as a developer

Hi, everyone. This time, I am studying new programming while thinking about my career in web and games. It's only been 3 weeks since I studied Java and C++, but I have a lot of worries Even if you follow the examples in the book as they are, there are many cases where it doesn't work, and even the very easy examples are struggling for hours. There are cases where it can be solved by slightly fixing it without thinking, but there are many parts where I don't understand why the error was corrected. When I ask a question, I don't fully understand basic words such as instances, methods, etc. I'm worried if I can develop it on my own. I wonder how other current developers studied and how they solved the problem if they encountered it!