The reality is that you can't. So accept that going in and realize your learning will be iterative.
You'll be overwhelmed, that's OK. Copy paste code until you get something working. Here's the key. At that point stop, go back and understand the code you copied, why it works, and then try to rewrite it differently now that you know what worked.
Metaphor for writing. Start with a quote, then paraphrase it. Do that enough and you'll start to be able to adlib and come up with your own solutions.