There is a create page from theme option, or just create the page and apply the theme template.
The theme file created is actually a template. It is an exact copy of the template you were using, with all of the contents removed. So essentially it is a list of the editable regions that existed in your template when it was created.
Then all your theme pages contain all of the editable content your original template did, but don't have any of the templated design itself. The code then gets the design from the template using php... it then updates all of the paths since the template is in a different directory and swaps out the editable regions from your theme page.
The only requirement is that the template and theme have at least one like-named editable region, otherwise there is no point, but really you can add editable regions afterward and create new pages just like you did before.
