Click on the board to aim your dart.

You might hit what you aimed for!
You might get a double or a treble.
You could get a outer bull (25)
or a bull's eye (50)

Once you get to 40 or under you need to hit a double to finish the game--
e.g. if you need 30 aim for 15 (and hope for double 15!)
You must finish exactly to complete the game.