Folio numbering was added much later, often long after binding, to help readers and referencing.
Usually, too, only the recto of each folio is written on. This image shows the full numbering 1r but you will usually find only 1 written in pencil in modern times on manuscripts from the 1400s.
As you turn over the page called 'folio 1 recto' you are presented with the page called 'folio 1 verso' or f1v. These web pages use that same numbering system. So you are now on page f3r, which is filename f3r.htm on the system.
Please copy your answers to your own notes