There are serveral different ways to minimize all open windows.

1. Use the keyboard shortcut Windows + D to minimize all open windows. 
   
   
2. Use the Shake method, if the option is turned on.
   
   Open SETTINGS -> SYSTEM -> MULTITASKING and move the Title bar window shake toggle to On.
   
   Now, when you click the title bar of an open window, keep the left mouse button pressed, and shake from side to side, all windows except the selected one will be minimized.
   
   
3. Click Show Desktop at the extreme far right corn of the screen, to the right of the time/date, is a hidden button.