What are the iCloud settings for Mail?

iCloud is offline all of sudden on my iMac. I checked the settings in Mail Preferences, and there is missing information. iCloud just worked. I never had to actually set it up the way I had to for other email addresses, so I have no idea or record of what the settings are.

I read a post in answer to someone else and tried to log out of iCloud in order to log back in--in the hope of getting the settings back automatically. But it would not do that. Asked me if I wanted to retain Contacts, but when I said yes, I could not click on anything else.

Also, something else strange happened. For the first time, I got an error message related to Facebook, asking me to enter my Facebook password in System Preferences. But it will not accept my password. No idea whether these things are related.

Can someone please help?