Context.xml in tomcat 5.5

[Avinash Kumar]

Hi all,
 Thier is a file TOMCAT_HOME\conf\context.xml in tomcat 5.5 ,what we have
to write in this xml file and when is this file needed,i made two sample web
application in jsp and servets ,i just deployed those in webapps ,i se the
java and tomcat home as required  and these application are running ,i just
want to know that when we have to configure this file.
Thanks