How have I configured to back up contacts, reminders and other services to the iCloud?

I have 4 apple devices; an iPhone, an iPad, an iMac and a MacBook Air Laptop. I am a great believer in backups. I backup my phone and iPad via Finder on my iMac. Both the iMac and the Laptop are backed up using Time Machine. .Somehow I have managed to back up Contacts, Reminders and Calendar’s to the cloud; all the other stuff is via the iMac/Finder. How have I configured to back up contacts etc. to the cloud?