I started playing chess last summer, and I've been building notebooks of things I learn from watching videos, reading some books and article and playing. These are not lines, but principles just beyond the prime basics -- things to look for, a checklist for moves and many other things. At some point very soon, I'm going to review them all then hopefully I'll stop being checkmate bait. So I advise people learning to use notebooks -- but also read them and revise them.
chess notebook. learning openings.

a good thing to do with notebooks (if you have a membership) go on the explorer and revise from there so you can see what the masters play in situations so that when you get in them you know what to play.

today I've gotten myself an A4 notebook where i'll note down opening lines and I've just done 3 pages on the Sicilian main and side lines. I assume other players one this site have a chess notebook for noting down lines they encounter so they know what to do next time. i'm asking what have you done with your chess notebook (if you have one). for example you may have put down patterns or things to do in situation x. maybe openings or middle games or endgames.
if you don't have one. why? and i strongly suggest you get one.
You could also consider freebies like Scid vs PC and Lucas Chess that let you build opening trees.

My "notebook" is a single, flat text, computer file. I use a fixed, formal format of my own creation so that attributes, temporal patterns, plans, situations, etc. can be quickly found by search on those descriptive text strings. It includes database statistics and my own statistics of various types. More recently I've been including complete games outside of my repertoire just so I can quicky find examples of games with certain attributes (like Anastassia's Mates, Fishing Pole Traps, "queen slaps," etc.). Of course I also include complete games of significance within my repertoire, too.

Old school

Old school
that's what i'm using now. it does work though.

I don't really have a chess notebook. I do have this chess opening app that can tell me what opening that person is doing

I don't really have a chess notebook. I do have this chess opening app that can tell me what opening that person is doing
that doesn't really tell you how to play against the opening. today I've written 3 pages on the Sicilian defence. now i can look at it to revise when i want. i strongly recommend you do the same.
today I've gotten myself an A4 notebook where i'll note down opening lines and I've just done 3 pages on the Sicilian main and side lines. I assume other players one this site have a chess notebook for noting down lines they encounter so they know what to do next time. i'm asking what have you done with your chess notebook (if you have one). for example you may have put down patterns or things to do in situation x. maybe openings or middle games or endgames.
if you don't have one. why? and i strongly suggest you get one.