Upgrading Mavericks --> Sierra
This is a slightly confusing Apple UI-fail.

Since Allan is partly or basically correct: 


  You downloaded it. You didn't install it. To install it, you need to
  go to you Applications folder and launch it. – Allan Oct 31 '16 at 1:01


Seeing that the confusion persists:     


  Can you be more specific? What is the name of the thing I need to
  launch? It does say installed (look at the pic). What does that mean?
  – user2429920 Oct 31 '16 at 4:04


Your picture displays "installed" for Sierra, alright.
You need to combine Allan's comment with the contents of this comment:      


  The name of the app is "Install macOS Sierra.app" or
  something along those lines – NoahL Oct 31 '16 at 4:16


That means: Your AppStore application has successfully installed the "Install macOS Sierra.app". That info is pictured in the banner you posted: you downloaded the installer completely and the installer is therefore marked as installed.

To actually install that new system as the system running your machine ("upgrade to Sierra") you indeed need to open the newly installed "Install macOS Sierra.app" in your Applications-folder. That will then guide you through the actual install after which your system will boot into Sierra.