It's hard to describe. In upper level math (real analysis and the like) in college I would write every single thing the professor wrote on the chalkboard down in my notebook. I didn't really study or do much homework, but copying down those proofs made the concepts stay in my brain.

Do you write when you do math? Math and handwriting are so intertwined in my experience, I can't imagine doing math past high school without at least jotting some parts of the process down.