You figure it out. I know that doesn't help much, but honestly, most of the learning is in the specifics.
Find a program and start following tutorials. Try to get an understanding of how the program works.
As you keep going, you'll start being able to figure out more for yourself. Most programs use similar ideas, but just execute it a little bit different ways, so some concepts from one program can translate to another.
Once you feel like you have a good enough idea of how a program works, make something small.
Focus on finishing things. Put it out there, get feedback.
Expect there to be problems, including ones you don't really know how to fix yet. It happens to everyone at some point, and early on it happens a lot.
Expect to get stuck procrastinating. Expect to be confused and overwhelmed.
Expect to have to cut out ideas you loved, and move forward with ideas that aren't quite as good as you imagined.
And expect that as time goes by, and you keep making and learning, those things will be less severe and less often.
And things will never be exactly as you imagined them. They always end up working out a little differently.
That's part of the process, and honestly, it's a part I enjoy. If it was exactly as you imagined, you wouldn't get the joy of discovering what the final result would look like piece by piece ^,^
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