Developing Object-Oriented software that deals with data from Relational Databases can be cumbersome and resource consuming. Development costs are significantly higher due to a paradigm mismatch between how data is represented in objects versus relational databases. Hibernate is an Object/Relational Mapping (ORM) solution for Java environments. ORM refers to the technique of mapping data between an object model representation to a relational data model representation. See Wikipedia for a good high-level discussion. Also, Martin Fowler's OrmHate article takes a look at many of the mentioned mismatch problems.

Although having a strong background in SQL is not required to use Hibernate, having a basic understanding of the concepts can help you understand Hibernate more quickly and fully. An understanding of data modeling principles is especially important. Both http://www.agiledata.org/essays/dataModeling101.html and http://en.wikipedia.org/wiki/Data_modeling are good starting points for understanding these data modeling principles.

Understanding the basics of transactions and design patterns such as "Unit of Work"[PoEAA] or "ApplicationTransaction" are important as well. These topics will be discussed in the documentation, but a prior understanding will certainly help.

Hibernate not only takes care of the mapping from Java classes to database tables (and from Java data types to SQL data types), but also provides data query and retrieval facilities. It can significantly reduce development time otherwise spent with manual data handling in SQL and JDBC. Hibernate’s design goal is to relieve the developer from 95% of common data persistence-related programming tasks by eliminating the need for manual, hand-crafted data processing using SQL and JDBC. However, unlike many other persistence solutions, Hibernate does not hide the power of SQL from you and guarantees that your investment in relational technology and knowledge is as valid as always.

Hibernate may not be the best solution for data-centric applications that only use stored-procedures to implement the business logic in the database, it is most useful with object-oriented domain models and business logic in the Java-based middle-tier. However, Hibernate can certainly help you to remove or encapsulate vendor-specific SQL code and will help with the common task of result set translation from a tabular representation to a graph of objects.

See http://hibernate.org/orm/contribute/ for information on getting involved.