Jackrabbit is a great implementation of JCR, and Liferay portal uses jackrabbit as its Content Repository for Search Engine, Document Library. The source code of liferay could be a great sample to recognize most of its advantages in practice.
However you can go directly to jackrabbit website and use the first-steps samples if you are a novice to JCR.

http://jackrabbit.apache.org/doc/firststeps.html