Double-click on the JAR file and then skip to step 6. If nothing happens, then open up a Terminal window.
Go to the folder that contains the download JAR file with the cd command.
Ensure that java is in your $PATH (or %PATH% for Windows). Most likely, it is, but if the next step says that it cannot find java , then ensure that your PATH environment variable contains Java. At this time, I don't have instructions for how to do this, but a Google search on that subject should give you insight for your operating system (even Windows has completely different ways to do it depending on the revision (95/98/ME vs. NT vs. 2000 vs. XP)). Mac OS X users don't need to worry about this step.