Please avoid tabs for indenting, and use the code button. I have edited your post partially and you can see how much better it looks. If you use Eclipse (which is probably a bad idea at this beginning stage), you can set options to convert tabs to 4 spaces automatically. You are probably better off using a text editor, however.
I think you will only understand it if you go through it with a pencil and paper. Try this simplified version first, and you will see how a loop runs once.Once you have worked out how that simpler version prints 3 thrice, you will find it easier to work out how the two loops work.
What part did you not understand? What did you expect that code to do?
Does that help? The outer loop says, "Do whatever is in my body, 5 times." The body is printing i and then running the inner loop, which says, "do whatever is in my body, 3 times. And that body is simply printing j.