The name of the function, what goes in and what goes out in most cases should be enough to get a good idea on what the function does.

It also helps to make a diagram of how everything ties together. Just boxes and arrows is enough.

When writing your own code, it takes a bit of experience to know when to put something in its own function. It’s very obvious when you’re replicating code. It’s also very common to cut things up when a function gets too big. Look for bits of functionality that you can give a good name.

I can strongly recommend the SponsorBlock extention (also available in revanched).