How to do 2-page on iPhone IOS 9.0.1?

How do I do the thing where you can mess around with 2 pages at once on my iPhone?

Added (1). @Danielle Apparently. In the details of the update it said "No need for switching back and forth between apps with our new 2-page feature!".

You can do that?

That's for iPads, not iPhones.