You can run the Jar directly, or have the batch file and the jar in the same directory and run the batch file. You also need Java installed.
I tried your game.
In general, I would agree with the others in the comments, but you did this from scratch in less than a month. That's impressive. The biggest change I'd advise is making the bullets bigger. May I ask why you chose to make your own engine, rather than using an existing one?
Though, for the sake of fairness, I'll rate your game the same way I would others.