How hibernate works

Or what it can do? Hibernate, residing on the application layer, supporting business logic.

• Mapping Java classes (Entity) with Tables in database. 
• Mapping entity instances within table entries. 
• Mapping an entity property within table fields
• Implementing persistence crude operations, and hiding complexity of SQL.  
• Maintain transactions
• Maintain dirty checking

Hibernate  manages how database connected, and data persisted via Entity manager. So for setting/configuring hibernate, "persistence.xml" is critical, which tells database URL, name, password, and mapping classes, and it may describe more than one database connection. One entity manager corresponds to one persistence unit.