All you need to know:
* Don't run into anything
* Click to shoot, but each wasted shot subtracts from your score
* ESC to quit
* Spacebar to start and pause/unpause the game.
* Your rate of point accumulation is proportional to your velocity, which is proportional to the distance of your mouse from your ship.
You should be able to double-click to start the program if you have Java installed, but if that doesn't work, you can run it from the command line by issuing java -jar TunnelGame.jar in the appropriate directory.