Opening apps in same desktop
On 10.8.5


  After you connect the displays to your computer, you can choose
  whether to use the displays as an extended desktop or for video
  mirroring. If you choose video mirroring, the displays each show the
  same image. If you choose an extended desktop, the displays form one
  large continuous desktop.
  
  If you are playing a DVD on a television connected to your computer,
  click the Arrangement button in Displays preferences and move the menu
  bar to the television. If you don’t see an Arrangement button, your
  computer is only capable of mirroring (showing the same image on all
  screens). For more information, see the manual that came with your
  computer.


On 10.9.3 (Mavericks)


  With an external display connected to your Mac, you can work the way
  you want. Each display has its own menu bar, and apps can run in full
  screen mode on each display. Want to use your HDTV as another display?
  You can easily do that with AirPlay and an Apple TV.
  
  Each display connected to your Mac can have its own windows and
  full-screen apps. You can spread out your work however you like.