How to back up my desktop's files

Hallo. I am computer illiterate. I want to upgrade the operating system on my desktop and laptop and I bought a WD My Passport to back up my files.
I have no idea how to do this. The instruction manuals don’t appear to give instructions for this and refer constantly to things such as My Cloud which I am unfamiliar with.
Why is it all so complicated?
How do I back up my files??
Thank you.

Hi ITilliterate,

You can follow the steps provided in below article to backup your computer on My Passport: