From FAQ :: How do I set up the template overrides?

All of my examples below assume
*You are using the english language. You get the idea for your own language.
*The example template name is /CUSTOM
After you successfully install Zen Cart, the CLASSIC template is used. So any folder named "classic" contains override copies that are used specifically with the CLASSIC template.

In the excerpt above, you probably missed that for the tutorial the name of the template will be called CUSTOM. So any necessary override files will go in a directory you create called "custom"

You only need to create template specific directories and use override copies of files when you modify a file to be different than those that come with Zen Cart.

The beauty of the override system is
(a) you always have a backup of the original file if needed,
(b) easier to see what files you modified,
(c) when you do upgrades it will be much easier.

Wrestle with the subject a bit. It's a very important one to understand, very learnable, and you will be glad you understand template overrides. Try re-reading that faq/tutorial again and see if it makes more sense now.