It's probably best to get someone to help you in person. See if you are near a Linux user group since they often supply installation help.
The method I always recommend is buy a new hard drive or SSD and swap it into the place of the old one, so you can swap back if something goes wrong. Then do a clean Linux install onto the new, empty drive.
Don't bother with dual boot, it's complicated and often goes wrong, and anyway you're trying to escape from Windows.
As for installation, you may have to go to your Bios setup to allow booting from USB. Then, on another computer, go here:
https://cdimage.debian.org/images/release/current-live/amd64/iso-hybrid/
Download your favorite iso image. I'll suggest "amd64-mate" if you don't have a preference, since it should be pretty familiar looking to Windows users. Then you want to write a bootable image to a flash drive. I only know how to do that with Linux, but https://duckduckgo.com/?q=write+iso+image+to+flash+drive finds a bunch of pages for other OS's.
Finally, plug the flash drive into your ASUS machine and boot. You should get a bunch of installation prompts and you can generally follow the defaults. It will install a lot of packages one at a time and take around half an hour, so do something else for a while, but also keep an eye on the install process because it will occasionally prompt you for something.
Come back after the installation finishes.