Hello, everyone!

I'm pretty much new to Zencart, and am still surprised on how so many people managed to "override" their Zencart files without actually messing up the layout itself. Anyhow, I recently downloaded Column Layout Grid for Product Listing addon, and still cannot figure out how to get it to work. The Product Listing - Layout Style isn't even there in my Admin panel.

Could someone please kindly explain step-by-step on how to properly install an addon without actually touching the finished layout (ie: CSS, modified PHP files, etc)? Each time I download an addon, the files there look just like what I already installed from the original Zencart installation in the beginning. How am I supposed to know which is which to override without messing up the complete modified files?

Thanks in advance.