I am not able to open iCloud from my settings, Sirs says I don't have iCloud installed what has happened?

I am not able to open iCloud from my settings, Sirs says I don't have iCloud installed what has happened? I have an email saying my device can't be backed up because my I cloud is full, and telling me to go to settings to manage it, but my iCloud button is in light grey instead of black and unresponsive.