How To Create API Based Web Service In Symfony2
Check the this article REST APIs with Symfony2: The Right Way by William Durand about Designing a REST API.
I think the best repo you could look at is at:
https://github.com/lsmith77/symfony-rest-edition
this is a tutorial
http://welcometothebundle.com/symfony2-rest-api-the-best-2013-way/
I believe the answers given above are not that introductory to the world of FOSRestBundle so I'd recommend this detailed getting started tutorial on how to properly setup FOSRestBundle with easy to understand examples on controllers, form processing and so on.