@Gary, Are you running on SaaS (ie. Odoo.com hosted) or on a local install (ie. on your own computer)? Basically there is a 'base' theme framework (including CMS, Ecommerce, etc.) that works as a fallback mechanism that can be modified by creating your own theme module to override or inherit and modify certain features. I'l recommend purchasing one of the tiers on the Indiegogo campaign for Odoo themes here: https://www.indiegogo.com/projects/bootstrap-themes-for-odoo-cms as there are some tiers in this crowdfunding campaign that include a developer/designer handbook which explains in detail how this works. The theme modules (from my understanding) can be installed on SaaS as well as in a local Odoo instance, so either way you can design custom themes to create a custom website for the Odoo CMS/E-commerce platform.