Before start this please ensure all (given below) the java packages intsalled in your system.

sun-java6-bin   
sun-java6-jdk   
sun-java6-jre

if not then install via ubuntu software center.After installing all java packages.

Step :1. Open terminal and type  “sudo apt-get install tomcat6” (it will automatically install the tomcat).

Step :2. Check the working of tomcat by browse http://localhost:8080/. It shows the message give below:

Step 3: Congrulation you have sucessfully installed tomcat server 6