Point the SM58 toward your source and away from unwanted sound; its cardioid polar pattern rejects much of what's behind it, significantly lowering the amount of stage bleed, monitor mix, or background noise that gets picked up by the mic.
Built into the SM58 is a pop filter, which helps control wind and breath noise without requiring an external pop screen. Of course, external windscreens are available should you choose to accessorize your SM58.