Just adding the menu item does not create the content area.
you need to create the content area in the power store admin, then create the page to display the content.
Click the green plus button next to content in the admin section to create the content area.
Click the developer notes link for the content area to get the code that will be needed to display it in a page.
Create a new php page, and add the developer notes to it to show the content area, your new link should point to this new page.
When you create a new page from the template, the name you give the page is the name that will be displayed on the menu. This cannot be changed once created.