@PsychrolutesMarcidus It’s definitely something that you have to practice, so don’t feel overwhelmed!
I personally don’t write a summary immediately, instead taking little notes of specific thoughts in the text I want to remember. Those little notes are in my own words. Then, I scan the notes to see how many talk about the same idea, and use my short notes as a framework to build a zettel.
It’s important that you understand the idea. If you lack understanding, it’s hard to write a zettel that encapsulates the idea well enough to sensibly use it years down the line.