Here's a quick overview of how to set up HDRi environments.
This tutorial shows you how to use HDRi lighting in Blender 2.78 and how to get more control of the overall effect the HDRi produces without even touching the compositor (though I still recommend you do for finishing touches). The video also contains a list of websites you can get HDRi's from in the video description.
~Mark 'BlendedMarks' C
https://youtu.be/7Of_VzWj7SE
