Main menu, first level (1)
This is for main sections (not individual views) and groups multiple related views/apps. This menu item has an icon.
Main menu, second level (1)
This is the sub sections or specific views of the first level main menu. This menu item has an icon.
Main menu, third level (1)
The is more rarely used but can be efficient for providing a kind of shortcut to functions or "latest used" items. This menu item has no icon.
This is for shifting between content in the same panel. Has no icon.
Often presented in tables with links. This guides the user to items or other areas in the application. Most often this have no icon.
Can also be used as a "split view" navigation, where clicking the link will present new content on a part of the page.
Be cautious – making too much navigation, can be confusing to the end user. Less is more. However, a navigation panel inside a pane gives room more options.