You want to run it from the command line, and it takes arguments too - the location of the compiled java program you want to run, plus any arguments that program itself requires. Running java on it's own just gives you it's usage instructions and nothing else. If you're trying to compile something, then it's javac you want, again from the command line and telling it what to compile. If your assignment requires this sort of stuff, I kind of expect them to at least tell you how to do this somewhere