Display Zoom - how is it activated?

How is the Display Zoom feature activated for the 6 and 6+? In settings? A gesture? Something else?

This is listed in:

http://www.apple.com/iphone-6/specs/

And shown with both standard view and zoom view about 2/3's of the way down this page:

http://www.apple.com/iphone-6/display/

 

Thanks for answering.

I assume this zooms all screens (i.e.) in apps like safari or just the home screens?