Understanding the platform an app intends to run on is important. This enables the designer to develop a deeper understanding on the unique user interaction, user interface elements, terminology and device characteristics in order to fulfil a high level of user experience.  

IOS

Part 1: Gestures in iOS

Upon turning on an iOS device, the user is able to learn 4 things.

1. The screen is touch based
2. User interface elements are touch based
3. The user will need to use fluid gestures such as touch and swipe to engage the user interface elements
4. The hardware buttons are secondary to the touch experience

There are 6 common gestures.

Tap
Drag
Flick
Swipe
Pinch
Random Gestures

Part 2: UI iOS Anatomy

Keyboard
Pickers and Date Pickers
Inputs
Tab Bar
Navigation Bar
Toolbar
Action Menu