Hibernate is an object relational mapping tool for Java platform and comes as open source. It provides powerful, ultra-high performance object/relational persistence and query service for Java. Hibernate lets you develop persistent classes following common Java idiom - including association, inheritance, polymorphism, composition and the Java collections framework.
Expertise in it
if you want to expertise in hibernate then you must read step-by-step tutorial provided by roseindia on Hibernate.
And run all the given hibernate examples to learn it quickly.