How can you access/open principled BSDF editor? Blender Version:2.79b
Cycles Render enabled

I have looked everywhere and I can't seem to figure out how to get the shader mixing editor (principled BSDF) to open.

I would really like to use it. Maybe I overlooked something simple. Please help. Thank you.

This is all I'm able to get. But I don't see shade mixer nor do I see principled bsdf.
Split your screen and make one window into a Node Editor. Then use Shift + A to bring a menu from the pointer and go to Shader -> Principled BDSF. You can also click on 'Search' once you've called the many via Shift+A and type 'principled' and it will be displayed on the results.