Click the 
button
Or click the button in the upper left corner of the title bar and select Minimize
Or right-click the window title bar and then click Minimize
Or press ALT+SPACEBAR+N (application) / ALT+HYPHEN+N (document)
Minimize reduces the application window or document window to a small icon at the bottom of the screen. To restore the window to its previous size, use the Restore command or double-click the icon.
To minimize the window:
Click the button
Or click the button in the upper left corner of the title bar and select Minimize
Or right-click the window title bar and then click Minimize
Or press ALT+SPACEBAR+N (application) / ALT+HYPHEN+N (document)