I read it a couple years ago. Lion describes his notekeeping approach in great detail. What kind of paper to use, what kind of pen to use (the one that has many colours; each colour has an assigned meaning), what binders to use. For a new paper enthusiast, some insight can be found here

Note that this book is old, and the author doesn't follow these techniques anymore (as far as I understood from talking through video calls). Btw Lion's notion of “hooks” (not described in this book) was one of the things that made me do Betula.