You have to set a breakpoint in your code. This can be done by doubleclicking on the left margin of your
Java src file editor. Once you run the application the debugger is invoked and you have to switch to the Debug Perspective in eclipse which it does by asking you to switch to debug perspective once it encounters a breakpoint.
Use eclipse help tool to for more information on the Debug perspective.
Also, I think you have to setup your project as a
tomcat project.