This newly-acquired leaf is from a choirbook, possibly created in Italy around 1500. Choirs at this time were made up of around 10-12 singers at the most, and as all singers read from the same book, choirbooks had to be large - in this case, over 600mm by 400mm.
The music is written in square chant notation on red 4-line staves with moveable C and F clefs. The chant is for the Dedication of St Michael, the Archangel.
Oral history advice and workshops to get you started, or hone your skills.