Look at the very top for the menu item Window, then go to UI Elements, here you can show or hide the various interfaces. When you learn to use the spacebar, you can go to Hide UI Elements and have just a viewport 
Hold the spacebar down and see what I mean 
Darkon
Red bellows of flame have blackened my stones
Convulsing my frame and cracking my bones
Hell's dragons of steel who roar in their chains
Crawl into my caves to suck out my veins.....
-The Mountain P.F.M.