WHAT IS PATH ENVIRONMENT VARIABLE AND HOW TO ADD IT

i just add this to my ~/.bashrc

export JAVA_HOME=/usr/lib/jvm/java-6-openjdk export PATH=$PATH:$JAVA_HOME/bin export CATALINA_HOME=/opt/apache-tomcat-5.5.26 export PATH=$PATH:$CATALINA_HOME/bin export ANT_HOME=/usr/share/ant export PATH=$PATH:$ANT_HOME/bin  $CATALINA_HOME/bin/startup.sh 

then

$ source ~/.bashrc 

it works