J2EE = Java 2 Enterprise Edition.
http://java.sun.com/j2ee/ Read introduction.
J2EE API's are totally different from J2SE API's. It can be used as an extension of the J2SE for Web based and Distributed Enterprise applciations using EJB (Session Beans, Entity Beans etc..), Web Technology (Servlets, JSP etc..) etc.
Please look at the J2EE tutorials:
http://java.sun.com/j2ee/tutorial/1_3-fcs/
Hope this helps