The Apple Watch is expected to be a very popular device. It will not make its debut in 2014, but smart developers are already planning out their apps for the device. Existing iOS developers can use WatchKit to extend the functionality of their apps on Apple Watch. Creating WatchKit apps is going to be straightforward. Each app has two parts: a WatchKit extension that runs on an iPhone and interface resources that are installed on an Apple Watch.
Apple has already posted a video that shows how developers can get started with WatchKit apps, glances, and notifications. You can find the WatchKit Programming Guide and other useful documents on Apple’s portal for developers.