Im new to Minecraft, and quite suddenly addicted. =p

Any ideas how I can use the classic (build only-- single player), full screen, and be able to save levels?

Ive been playing the browser version, but wanted to full screen it (of course). I couldnt figure a way to do that, so I DLed v.6.6.0 and couldnt save (greyed out). Then I tried 5.6 because I read in another post that one can save. But the button was greyed out as well.

To launch, I enter my credentials and click "Single Player" 

Thank you so much.