to commonly asked questions.

Am I on iCloud?

Our other iMac is not connected to my iCloud. And I couldn’t figure out a way to get it done. Is it because it hasn’t been updated in a while? I think we are running version 12

If you go to the black apple and select “about this Mac” it will tell you what operating system you’re on. iCloud started becoming fully implemented into the Operating system by 10.12 so if you are on MacOS 10.12 it will talk to the cloud. You would just need to check in your system preferences under “iCloud” to make sure you are signed in with the same appleID you are using on your phone and other computer.
This image is a theme.plist hack