Here are some very useful windows shortcuts. This are mostly for newbies but they can be very handy.

Minimize all windows (show desktop) - Window key + D

Switch through open windows -Alt + Tab

Take a screen shot of the active window (in clipboard) - Alt + Print Screen SysRq

Open your start menu - Ctrl + Esc or Windows key

Closes an active window (If no window open prompt to shutdown Windows) - Alt + F4

Displays the main window’s System menu - Alt + Space