Usually from the website of the distro you have decided upon.
First a few vocabulary definitions (for someone "who knows nothing"):
Do you put it on a CD-R? A DVD-R? I.e., before installing it on your C: drive?
Typically, yes. You can also use a USB drive, if you know how to make it bootable. Many of the distros can be run directly from the CD/DVD without having to remove Windows first. This allows you to test drive various distros until you find one you like. Keep in mind that performance will take a large hit due to running from an optical drive.
For users looking to switch, I have heard good things about Zorin OS, PCLinuxOS, and Mint. Those are all Debian-based distros (distros that began life as a fork/modification of Debian), but I personally prefer rpm-based systems.This is strictly a personal preference as I started with Red Hat (in 1994-ish) and just stayed with it.
My local Computer Store sells Linux DVDs for $3. I usually start with a fresh HD so going back to the old system is trivial.
Just wondering out loud, if things have changed, ref: WordPerfect & Linux. Maybe just run Linux with a virtual windows program, similar to Windows-7 / virtual machine?