A complete documentation is available that you can search from here :

Shortcuts

• Two minutes to get Sonar up and running
• Full Installation guide
• Getting started with Sonar

Use cases

• Technical debt: Evaluate your technical debt with Sonar
• Authentication and Authorization: Securing access to projects in Sonar
• Sonar Time Machine : Learn how to replay the past
• Package cycles : Fight Back Design Erosion by Breaking Cycles with Sonar
• Coupling and Cohesion : Clean Up Design at Class Level with Sonar
• Portfolio management: bring a new dimension to Sonar with the Views plugin.
• Sonar Light : the low calorie mode for Sonar
• Unit tests : manage unit tests and improve code coverage
• Code Review: quality of Apache Sling using Sonar
• Continuous Integration: A Hudson plugin for a closer integration with Sonar.
• Having fun: The most sexy plugin of the Sonar forge

Others

• “Contrôler la qualité de ses projets avec Sonar”, a french article by Romain Linsolas.