If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
When you hear the whistle, be throw a bag to the next customer. But watch out for obstacles along the way. Running into things will cause your energy bar to decrease.
Tip: Bottles and hearts will replenish your energy bar, so pick them up! Also, pick up money for points.
Arrow keys Left/Right - To move.
Arrow key Up - To jump.
Arrow key Down/Space bar - To throw.