Manage App Set Up Navigation Page Explained

The "Manage Application" > "Set up" > "Navigation" page allow you to select the options on the left hand navigation menu. You can select what you want to appear on the left hand navigation. You can also drag and drop to rearrange the icon on the left hand navigation. 

If you want to have an icon to open an external url, enter the external label and link, click "Save". You can add up to 3 external links.