There are many different backup methods, software solutions, and doctrines. Generally all agree that you should keep at least three copies of your important files in three different places. Many will suggest you keep weekly copies of your files, in case of accidental deletion or corruption so that older versions can be retrieved if needed.
If you are storing your files on iCloud, Onedrive, or Dropbox (or a similar service), you're already backing up to one location.
For the best recovery option, you'll also want a full system backup, so that you can go back to your computer as it was on the date the backup was made to retrieve your files, or recovery your system in full in case of infection or disaster.
Below are some recommendations for creating such a backup. For best results, hire tech support to manage and monitor your backups for you. This gives you the best insurance against losing all of your information, financials, photos, and memories to virusus, scammers, or even just a power surge which damages your computer.
To make a full system backup, you'll need an external USB hard drive at least as large as the hard drive on your computer. Preferably, it'll be 2x or 3x the size so that multiple versions of backups can be kept on the same drive.
macOS and Time Machine
Windows 10 and Macrium Reflect