In addition to Reminders, Calendar is another stock app on the iPhone, iPod touch and iPad designed to help users organize their daily, weekly and yearly schedule and be more productive.
With 3D Touch on the iPhone 6s and iPhone 6s Plus, it's easier to accomplish things with fewer taps.
Though not as developed as in other stock apps, Calendar's 3D Touch implementation permits you to add an event from the Home screen and glimpse what's coming up next on your schedule. In this tutorial, you will learn about 3D Touch shortcuts and Peek and Pop gestures in iOS 9's Calendar app on the iPhone 6s and iPhone 6s Plus.