C|

The cantus in particular is very easy, very good for beginners to early notation. 

No ficta. 

Repeats:

(A BB C) + A

i.e. play ABBC as many times as desired, for as many verses as desired, then finish with a final A.

A is the "Chorus", BBC is the "verse". Structure is chorus-verse-chorus-verse-chorus. 

Sprightly, so be sure to count in semibreves or breves.

Structure:

At the end of the piece is a custos and "ut supra" (as above) and "Sio douesse, etc" (referring to prior words).

So the structure seems to be

A (B CC D)x B with x being as many verses as you wish (three present). That is A is an introduction played only once, B is the "chorus" and CCD is the verse.

Simple and pretty.

I don't know what the curly symbol over each note in the second section means. It looks rather like the fermata/corona used at the end of other phrases, only without the dot. But I can't tell from context what that would mean when applied to every note in a phrase.

The repeat structure also isn't  clear. My guess is:

(ABCC)x AB

That is, AB is the 'chorus', CC is the 'verse'; repeat as many times as needed for the words, then finish with a final 'chorus'.