How can I use Hibernate with TomCat 5.5???????

I don't know what to do anymore... I am trying to connect at my DB into the MySQL by the TomCat 5.5, using JNDI.
I didn't understand what is hibernate.jndi.url and what name I need to give at JNDI, I rad everything in the web and I didn't found anything that can explain to me what is it.
That is my result into the browser when I try to acess my servlet by the index.jsp. Please help me! I need to do this! If you can say me where I can find a good book!

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Error instantiating servlet class MeuServlet
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:14 smilie

org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
java.lang.Thread.run(Unknown Source)

root cause

java.lang.NoClassDefFoundError: org/hibernate/Session
java.lang.Class.getDeclaredConstructors0(Native Method)
java.lang.Class.privateGetDeclaredConstructors(Unknown Source)
java.lang.Class.getConstructor0(Unknown Source)
java.lang.Class.newInstance0(Unknown Source)
java.lang.Class.newInstance(Unknown Source)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:14 smilie