Apple offers iCloud Backup for iPhones and iPads but not for Mac computers.
It is possible to sync data from a Mac to iCloud if you turn on those options (e.g., iCloud Photos, iCloud Drive including the Desktop & Documents option). Syncing has some of the benefits of a backup (and the benefit of being offsite) but is not the same as a backup. Major differences include the fact that not everything on your Mac can be synced and the fact that if you delete something, accidentally or otherwise, there is only a limited time period (30 days in most cases) during which it can be recovered.
Synced data will be synced with iCloud and with any other Apple devices (using the same Apple ID for iCloud) where you have the same syncing option(s) turned on.
Also see: https://support.apple.com/mac-backup
And more information on syncing in:
Set up and use iCloud Photos - Apple Support
and
iCloud Drive FAQ - Apple Support