Apple's latest "one more thing" was a doozy: A high-tech watch that CEO Tim Cook hopes will "redefine what people expect" from a wearable device. The watch does much more than tell the time -- but what exactly does it do? And what can't it? The $350 Apple Watch is meant to be worn throughout the day and relies on its connection to an iPhone for much of its functionality. It can track health activity, communicate with friends and run a wide range of apps. It can even make retail payments.