The artist went into a great amount of detail in his thinking for this prestigious and challenging project, though sadly none of his work was ever put into action. Leonardo da Vinci acknowledged the superior quality of several designs that came from Milanese court architects and there work was preferred also by those making the final decisions.
Several of the items on this paper capture the dome from different angles plus there is also a bird's eye view for the planning of the exterior. There was a whole series of similar drawing work completed, though many did not survive to the present day, due to the fragility of the medium and also the lesser importance that artists would place on their study artwork.
There is also a small amount of textual notes in the bottom left of the paper which would serve as a helpful addition for art historians who could learn more about this piece from that. Study drawings frequently have small handwritten notes on them, such as decisions over elements of a composition or perhaps a philosophical muse that would explain more about the artwork.
Da Vinci would experiment with many different tools for his sketchwork, such as different shades of chalk plus pen and charcoal. The Renaissance masters were famous for their ambition and will to learn new skills throughout their lives.