The difference between cart weever and eCart is cart weever is a prebuilt commerce solution, whereas eCart is a tool to create the shopping cart functionality.
Cart weever is already pre built php pages.
eCart is a tool used to create a specific part of the project (the shopping cart).
It sounds like The linda.com videos you are referring are not based on creating an eCommerce solution, but using a solution that has already been built.
we Also offer Power Store which is a prebuilt solution and contains the admin pages already. eCart was used to build power store, so was Security Assist, and Data Assist (they where used for crating the admin functionality).
Data Bridge is the tool that you use to create the Catalogue and product admin pages. see this tutorial for details on creating the Catalog and product admin pages:
after creating the catalog and admin pages, you can add the eCart add to cart functionality:
If you arent seeing the pages after running the wizard, it sounds like you do not have your site defined correctly. See this tutorial for details: