While you can override any template using the methods described in Custom Templates, in the backend user interface you can add and edit custom templates for listings, products and questions directly.
On top of that, you can have multiple templates for those 3 views and assign specific templates to each product/page/question.
How to edit templates
See Templates in the ConfigBox menu and add a template. You'll be asked for a name and the type of template you make. You can copy/paste the default template code from the links in section 'Default Templates'
How to select templates for products/pages/questions
Products: See section Display in Product Detail Pages
Pages: See section Display
Questions: See section Misc