How to manage iCloud storage? I don't understand ...



Apple emails my iCloud 5GB is nearly full. From the above screen, it's 833.7MB + 450.2MB, why only 118 MB is left? 

How can I check how/where the space is consumed?

p.s.  Settings > iCloud > Backup is OFF

Here is the screen from my MacBook:



Here is the Photos app setting:
@Tetsujin is on the right track - iOS 9 was released with some bed bugs that caused iCloud backups of iPhones and iPads to fail, and often left junk around in iCloud.  

In the bottom of your second picture this is confirmed in the graph - you can clearly see backup's (in yellow) are consuming the lions share of your storage.  The easiest thing to do is turn of iCloud backup on all your devices and then delete the backups if they still show up in the settings app before re-enabling iCloud backup.  Some people have had to open tickets with Apple to get them to clean out their backups.  Thankfully for me once I updated to the latest version of iOS 9 all I had to do was turn off iCloud backups and then turn them back on and my devices started backing up to iCloud again and my backup storage consumption on iCloud dropped dramatically. 

Good luck!