there is not a tutorial that shows the whole process.
you are getting to caught up in using the presets and not really thinking through what the presets are doing.
the admin:
The admin preset is creating the following pages:
admin/search.php
admin/results.php
admin/details.php
admin/insert.php
admin/update.php
admin/delete.php
the public preset is creating only the basic pages at the site root:
search.php
results.php
details.php
The database you use really doesn't matter, the eCommerce database is a good starting place, but you may need to modify it to suit your needs.
after you have created the admin and public pages you can create your template and apply it to the pages. there options on how you do that, which to use depends on which works best for you.
you will want to use security assist to restrict access to the admin pages.
then you can add eCart to the public pages.
