This note collection (or 'vault' in Obsidian terms) is separated into 'Permanent Notes' and 'Literature Notes' (loosely based on the Zettelkasten style of note-taking). 'Permanent Notes' are notes about general topics or ideas, whilst 'Literature Notes' are notes on a specific resource (e.g. book, poem, article etc.).
The Permanent Notes section is further divided into 'Permanent 'Topics and 'Permanent Zettels'. Permanent Topics are larger notes about more general or broad concepts, whilst 'Permanent Zettels' are more concise or singular ideas or thoughts.
Besides those categories, these notes have no other hierarchy or greater organisation structure. I use tags and links between pages, as well as just searching what I need, to find anything inside my notes. I'd recommend using the graph view or search function to look around and see what interests you.