Inorder to understand hibernate, your pre-requisites are you have to know JDBC concepts, hibernate is nothing but a framework which we used to connect to different different databases,and for resources search in the net which explains hibernate
i know one website,
JSP Tutorials,EJB Tutorial,JDBC Tutorials,Free Java Servlets Tutorials, WAP Tutorials, Spring Framework Tutorials, J2EE Tutorials, BioInformatics Tutorials, Java Server Faces Tutorials, Jboss Tutorials, Hibernate Tutorials, XML and MySQL Tutorials
there are so many pdfs will be available, go through that also
you can find pdfs in
Ebook Search - Pdf Search Engine
I think it will help you