Slingo is a casino game from Zynga.
The cheat is included in the leethax.net Firefox extension.
Click the LeetHax button on the right to access the cheat interface.
Hover your mouse over each option to see a detailed description.
If clicking the LeetHax button does nothing, refresh the game; the game should resume from where you left it, and the LeetHax button should work again.
Energy can't be cheated directly. The server will not accept scores, provide reel data etc. unless energy was spent to start the game.