Kalvinder,
JPA is a persistence API, and Hibernate is just one implementaion of that API.
You should definitely use JPA, but you do not need to use Hibernate. The vendor implementation that you use is up to you, and will depend upon your preference. I usually recommend TopLink Essentials to people that are starting out since a) it is the Reference Implementation and ships with the Sun Glassfish server b) it is the easiest one to install and get going c) it was created by Oracle and I work for Oracle :-). It is just a couple of jar files and can be downloaded from the Glassfish site
here.