Use Dropbox for backing up files. There are two options: upload files manually or sync them.
File backup
A backup is nothing more and nothing less than a copy of something elsewhere. That place can be an external hard drive or USB stick, but it can also be online. With an online backup of files, there is no risk of loss, theft or damage to, for example, the external hard drive. You can make an online backup with Dropbox, among other things. In the article “What is Dropbox?” discuss what this service entails.
Manual backup
With a manual backup, the original file is on the computer and the user copies it to Dropbox themselves. In this case, the files will not be synchronized. That means if the file is edited in one place, it will remain unedited in the other place.
Learn how to upload files through the website in the “Working with Dropbox over the web” article.
Sync files
If the Dropbox program is on your computer, a Dropbox folder will appear in File Explorer (Windows) or Finder (Mac). All files in this folder are also stored online in Dropbox. They are synchronized. So one file is available in two places and changes are saved in both locations. Note: if you delete a file from this folder or from the cloud, the file will be deleted in both places.
The Dropbox program is available for Windows (Install Dropbox on Windows) and the Mac (Install Dropbox on Mac).