Adding a custom module to a ZenCart website

Zen Cart seems to be a different beast, something which I'm not use开发者_开发百科d to. I need to know how to add an age verification form within the install. The typical way of creating a file to use and linking it within the header file doesn't work. There's also this specialized way of adding pages, which I tried to do via reading the wiki, but that didn't work either.

Has anyone tried to add a custom JavaScript or PHP Module to a ZenCart install? Is it possible?