JBoss.orgCommunity Documentation
Suppose that you are running the local host at port 8080 (http://localhost:8080/), the path of the API will be:
REST API:
http://localhost:8080/social/social/rest
RPC API:
http://localhost:8080/social/social/rpc
To learn what you can do with the APIs, have a look at the specification. If you are developing in Java, you can use the opensocial-java-client.