Debug means to fix (remove the bugs). So if your program has a problem you would debug it. There are lots of different ways of doing that. Sometimes looking at the code is all you need to do to find the problem. The next step would be to put a bunch of "println" statements into your code, and use them to figure out what the problem is. The best way to debug is to use a "debugger". Some debuggers are command line ones, like jdb, and others are graphical ones. All of them are suppose to help you by showing you what you program is actually doing. Most IDEs have built in debuggers.
Please ignore post, I have no idea what I am talking about.