First you need to create a custom page (Miscellaneous > custom pages)
Then link to it using the following in web_menu.sitemap
<siteMapNode url="~/t-enter_your_custom_page_id_here.aspx" title="Delivery Charges" description="Delivery Charges" />
This would add the link to an existing dropdown, but if you wanted it on its own 'tab' then add </siteMapNode> to the end e.g.
<siteMapNode url="~/t-enter_your_custom_page_id_here.aspx" title="Delivery Charges" description="Delivery Charges" />
</siteMapNode>
Also this menu is cached so you will need to restart IIS or recycle the application pool after changes are made.