How do I know if my macbook is using its NVIDIA graphics / display?

I see my integrated graphics card listed when I go to 'About this Mac'.
Macbook Pro
15-inch, Mid 2012
OS X El Capitan
Processor 2.3GHz Intel Core i7
Memory 16GB
Graphics Intel HD Graphics 4000 1024 MB
500GB SATA hard drive

But what is the deal with my NVIDIA dedicated graphics card?  Can I make it my primary and the integrated Intel HD Graphics secondary?  How do I know if it's being utilized when I watch movies or play games?

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Kyle SantosQuality AssuranceAsked:
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You can download a third party application which will put a notification in the menu bar to tell you which card you are using:
Alternatively, open Activity Monitor (which you can find in /Applications/Utilites) and click on the Energy Tab. Any apps which are using the high performance graphic card will show as "Yes" in the column "Requires High Performance Graphics Card".

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By the way, the  gfxCardStatus app linked above will also allow you to force the computer to use whichever graphics card you choose, but running on the Nvidia card will run your battery down more quickly. Also, there is probably no advantage to running the Nvidia card on applications which don't demand it.
Kyle SantosQuality AssuranceAuthor Commented:
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