Please Help, How Do I back up my Mac onto the My Passport?

Have bought a WD My Passport for Mac and I have plugged it in and downloaded the software but having never used an external hard rive and with the instructions in the downloaded manual not making sense (not a techy).
How do I go about downloading all the info on my mac to the hardrive?

Sorry for such a basic question but I bought this on the Amazon reviews saying it is very simple to set up.

Many thanks for any help!

Option 1) You can copy/paste data into it like other external hard drives.

Option 2) Install WD Backup for automatic copies.

Option 3) Use Time Machine, which is a part of your Mac and does not need an additional installation.