how to start to build an apple watch app ?

To start building an Apple Watch app, you can leverage Apple's native SDKs, which provide all the necessary tools and frameworks. Here are some steps and resources to help you get started:

1. Use Swift and SwiftUI: Apple's SDKs allow you to use Swift and SwiftUI to build apps for watchOS. These tools enable you to create highly integrated apps that feel like natural extensions of the user's device.

2. Xcode: Utilize Xcode, Apple's integrated development environment, to develop your app. Xcode provides a comprehensive suite of tools for building, testing, and debugging your app.

3. WatchOS 11 Features: Take advantage of the new features in watchOS 11, such as expanded capabilities of widgets and live activities. These features allow you to create more timely, contextual, and functional experiences for users.

4. Live Activities: If you have already implemented live activities in your iOS app, you can extend this functionality to Apple Watch. The system leverages your existing code to offer a live activity experience on the watch.

5. Resources and Documentation: Refer to Apple's Human Interface Guidelines and other documentation to understand best practices and design patterns for watchOS apps.

For more detailed guidance, you might want to check out the session Platforms State of the Union (49:30) which covers watchOS and its new features. Additionally, the session Bring your Live Activity to Apple Watch (03:22) provides insights into customizing live activities for Apple Watch.