My iCloud says that it is full because of Photos and Backup. Why are Photos and Backup two different things?

I would really like to backup my phone, but in order to do that, I have to make more space in my iCloud.

My iCloud currently is filled with Photos and Backup. I think that if I delete some of the photos, the Photos would take less space but is there a way to decrease the Backup?

Please help me with this problem! Thanks.