Apple offers iCloud Backup for iPhones and iPads but not for Mac computers - or for Windows computers.
It is possible to sync some data from a Windows computer to iCloud if you turn on the iCloud Drive and the Photos syncing options and that 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 computer 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: Set up and use iCloud for Windows - Apple Support