How do people study by writing notes?

Every time I watch those study vlogs or timelapse videos of people studying they're always writing down in their notebook, I don't understand how you make that method so effective because most of the time I find myself forgetting everything I wrote down the day after. I find that explaining it out loud genuinely helps me retain the lessons way way way better than note taking does.

I'm interested with how the note taking method works, because all I see is just mindlessly writing down information from the slide. I hope people also have saying things out loud as their most useful study method, although I find myself prone to being burnt out more because of it.