well i'm not using ubuntu but web manager should be more or less the same across the distros.Anyway you shouldn't use webmanger for single
jsp's
firstly do you get the welcome page come up at url
http://localhost:8080/index.jsp
if you can see that start by putting say hello.html (which has <h2>hello world </h2> between the body tags) into the ROOT directory of tomcat; then putting
http://localhost:8080/hello.html should show "hello world" in your browser. Thats a start