If you have iCloud Drive turned on in your Mac, it will (or should) automatically anything you save to or move to the iCloud Drive folder in Finder; if you also turn on the Desktop & Documents options it will do the same for everything in those folders. If you turn on iCloud Photos, all of the pictures in Photos should also sync. See the follow for more information.
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.
Also see: https://support.apple.com/mac-backup
And more information on syncing in:
Set up and use iCloud Photos - Apple Support
and
Access and manage your files in iCloud Drive - Apple Support
and
Add your Desktop and Documents files to iCloud Drive - Apple Support