A quick overview:

Windows Store – For customers, it starts with the Store, their one-stop-shop for Metro style apps. To get into the Store your app is reviewed for both technical and policy compliance, including security checks. After it’s published to the Store, your app will be rated and reviewed by the community. Together, the onboarding process and community reviews help create an environment in which customers can try apps with confidence.

App install – Windows 8 handles all the details of deploying apps on your behalf so your customers don’t have to worry that installing, updating, or removing one app will adversely affect other apps.

SDK – The Windows 8 SDK for Metro style apps provides a well-defined set of APIs that help you build reliable apps that conform to the Store onboarding requirements and provide the best experiences for your customers.

App container and capabilities – Windows 8 provides a greater degree of separation between apps than was possible with traditional desktop apps, so you can build apps that interact with each other in more predictable ways, giving customers a more consistent experience.

http://blogs.msdn.com/b/b8/archive/2012 ... -apps.aspx