3D Touch or Force Touch, as it is commonly called, is one of the advanced features innovated by Apple since iPhone 6S. To answer the second question, this feature is only available in iPhone 6S and above, so to use it you will have to get one of those. Till now, there were press and long press options to get certain tasks done on touchscreen devices, now Apple has added force into equation as well. By applying little extra force irrespective of time, a list of important functions pops out without even opening the app. Apple calling it Peek and Pop or Quick Action. To illustrate, suppose you want to take a selfie, instead of opening the camera and flipping the camera to front camera, you simply press the camera icon a little harder and tap on take selfie. Also, some of the most popular applications also support the same as Whatsapp lets you go directly to a list of recent chats, search chats, start a new chat or read starred message without even opening the app itself. So, it definitely is a good feature to have in a phone to save a lot of time and for convenience.