Microsoft released a draft of a document designed to educate you on what extensibility is available for the LightSwitch product, and to illustrate the various extensions types that can provide entry points into extending a LightSwitch application.
The document also contains "recipes" for creating the various extension types so you can get started building extensions for the LightSwitch community.
"One of the big features of LightSwitch is the ability for professional developers to write extensions to provide even more capabilities for the LightSwitch developer than what they get out of the box. A way to think of them is like add-ons. Extensions can be used to interact with the user directly, or to do some work behind the user interface such as data access.
In LightSwitch there are 6 extension points: Controls, Screen Templates, Business Types, Themes, Shells and Custom Data Sources."
In addition to the cookbook Microsoft is also providing a blank extension solution to help you get started: