[Analogus]

Mencken:

Folder ≠ Collection

Main differences:

A book can exist in just ONE folder. For removing the book from one folder you have either move it to another folder or delete the book. It's a question of 'to be or not to be'. Folders are a 'must'. No computer/reader/PC without folderstructure. A folder is like a bookshelf. A specific book can oinly be in one specific shelf.

A collection is something you can use additionally to folders. Collections are optional. Regard it as a bibliography. A book can be assigned to no/one/two/more collections as real books can be found in no, one or more bibliographies. Regard it as a second possibility to bring order in your books.

And how about the situation on your ereader?

Well, your reader is more focused on collections, not on folders. Technically books are stored in folders. But without additional software (for expample PRS+) you will not see this folders on your reader. You will see folders when connecting the reader to your PC. With/on your PC.

Last 3 books:

I think you're wrong. What you see are the last 3 added books, not opened.
If you do not want to see the last 3 added books - that's another topic. The last 3 added books have nothing to do with folders or collections. They are, well, the last 3 added books. Indebendent from whatever folder, collections, ...

If you really do not want to see this and instead, say, 3 books of a specific collections or the last 3 opened books or whatever - you will have to install PRS+. This gem of software can manage this 3 books, let you choose to open books from folders OR collections, and much more.

A.