What is the "Super" key?
This key can usually be found on the bottom-left of your keyboard, next to the Alt key, and usually has a window/squares icon on it. It is sometimes called the Windows key, logo key, or system key.
If you have an Apple keyboard, there will not be a Windows key on your keyboard. The Cmd (Command) key can be used instead.
The Super key serves a special function in Unity. If you press the Super key, the Dash is displayed. If you press and hold the Super key, an overlay showing many of Unity's keyboard shortcuts appears until you release the Super key.
The Super key can help you do even more than that, though. To learn about more uses for the Super key, see the page.