You, as the sheriff of Dodge (the bullets) City, must stop the bandits getting away ith the bags of money from the City Bank, and freeing their comrades in jail.
But stopping baddies takes it out of you a bit, so you have to keep an eye on your 'Thirst Level'. If it gets too low you can always pop into the Hotel for a quick drink with the lads from the O.K. Corral.
If your ammo gets too low, just walk over the body of a dead bandit, before he disappears and you will get more ammo.
Keep an eye out for Neddie, the bandits' faithful horse. If you get in his way, you will be trampled.
Make sure the bandits do not take all the bags of money. If they do, the people of the town will hang, draw and quarter you (and then whatever's left, they will feed to the vultures).