Some Windows keyboards have additional keys on the same row as the space bar.
There are two 'windows' keys to the left and right of the space bar and an 'application' key to the right of the rightmost windows key.
Used in combination with another key, you can perform some common tasks with a keyboard shortcut.
Windows Key + E
Open Windows Explorer (note this is not Internet Explorer)
Windows Key + R
Windows Key + Tab
Tab through all applications on the Taskbar
Windows Key + F
Find Files or Folders
Windows Key + M
Minimize all open Windows
Windows Key + <Shift> + M
Maximize all Windows (Undo minimize)
Windows Key (all by itself)
Open the Start Menu
Windows Key + F1
Some programs will use this key for application menus. It is equivilent to right clicking.