There are multiple steps required to debug a java program in eclipse such as:
- Setting breakpoints
- Starting the debugger
- controlling the program execution. For line by line use F6 and F5 to step into a method
- Evaluating variables etc
Putting everthing here will make the answer too long. I advice you to follow this tutorial :
http://www.vogella.com/articles/EclipseDebugging/article.html