It's great some people's brains here work entirely by doing and they can boldly proclaim they don't need any notes...
As if spoken in the voice of the professor from back to the future: "Notes?! We're I'm going I don't need notes!"
So ya, they may not need notes, but I do!
My brain absolutely requires notes.
And I re-read them periodically, and that helps refresh my brain on concepts I just learnt last week, as well as concepts I learnt a long time ago.
FOR EXAMPLE...
Working on a networking project recently, I was able to pull out my old CCNA notes from about 5 years ago, and after spending a few hours re-reading them was able to refresh my brain on those topics I spent a lot of time and hardwork learning 5 years ago.
Without my notes to refresh those old neural-networks, I would have lost a lot of that knowledge, and had to re-learn it. But my notes triggered all the memories--most of them!
Essentially, I use simple notepad text files.
The top portion usually contains lots of great links on the topic.
The other parts are organized into logical sections like examples of concepts of object-oriented-programming in that language (complete with examples I copy/paste), variables, GUI options, functions, memory-pointers usage and examples, list of header files and compiler codes, etc...
I use a few rows of long dividing lines between major topics...
I list each topic with an underscore so I can rapidly search the textfile, such as "_ POINTERS" or "_ LOOPS" etc...
And then minor topics with that section are nicely divided with shorter lines.
Also: I have a misc section at the end where I copy/paste portions of great comments and explanations from here on Reddit, and from programming blogs, etc...
Finally, if there is a really great reddit post with tons of great comments, I just capture the entire webpage as an image file, with something like the "GoFullPage" extension in the browser, and then give the file a name by topic, such as:
"C++ Sharing Process Output with Python"
or
"C - Bitwise Operations"
or
"C - SAMPLE - Arrays with Nested For Loops"
That way, in the file folder, all the image copies of screens relating to C line up by filename, and everything for C++ lines up, and likewise for other topics like "Bash -" and "Python -" etc...