Can someone elaborate this for me please?

Well if you mean that you need to know what it wants you to do you have to match the description to the shape. If you want the answers here:
1-d
2-e
3-a
4-b
5-c
I’m most certain on all except maybe 2 but I’m still pretty sure

The gregorian chant was a major cultural milestone in the middle ages. it was one of the first codified forms of music meant to be played as written, where previously it was difficult to mass-produce and disseminate any music. what's more, these chants were also some of the first examples of musical notation: the notes and bars of today's music sheets are a reflection of centuries of evolution beginning with these chants. it became official throughout the entirety of the catholic church, meaning that nearly all of europe followed this musical notation and styling.