I can't remember if I zipped or rarred them when I built it last. Either way, you'll need to extract it first (get WinRAR, it'll save you time in the future either way).
Once you've done that, open up a command-line, use cd <path> to get to where you installed JavaOp, and type
java -jar JavaOp2.jar. If you have any questions (the commandline can be intimidating!
or get errors, hit us back.