Go to Settings->Manage Templates in your SunShop administration area.
To add new pages, you must first provide write permissions to your theme folder (CHMOD 777) and all folders and files within it or specifically to the /themes/YOURTHEME/ folder. Start by going to the "Add New Templates" link & click the "ADD" button/icon, once you have entered your template name. You should now be able to select your new page from the templates dropdown. You can immediately begin adding your content/html.
Note: If adding content pages, add the prefix "page_" to your template names (See image.) and you can link to your pages from anywhere within the shop.
(Example: <a href="index.php?l=page_view&p=new_template" target="_parent">Link to New Page</a>)
We also have a detailed tutorial on how to add additional pages within Sunshop at our Knowledgebase: http://my.twt-inc.com/knowledgebase/35/Adding-additional-pages-within-SunShop.html