iPhone 6s introduces an entirely new way to interact with your phone. For the ﬁrst time, iPhone senses how much pressure you apply to the display. In addition to familiar Multi‑Touch gestures like Tap, Swipe, and Pinch, 3D Touch introduces Peek and Pop. This brings a new dimension of functionality to the iPhone experience. And when you use 3D Touch, your iPhone responds with subtle taps. So not only will you see what a press can do — you’ll feel it.
For general information about 3D Touch, go to Apple's webpage. Be sure to watch the video on Apple's webpage as it not only shows the new 3D features but it also shows the inner workings of the iPhone 6s that make these features work!
Scott Davert explains 3D Touch and how VoiceOver interacts with 3D Touch in the AppleVis article, The VoiceOver User's Guide to 3D Touch on the iPhone 6s.
For step-by-step directions go to Apple's Support's accessibility page, Use 3D Touch with VoiceOVer and Zoom.