Comprehensive vs collision coverage: what's the difference?

Both cover damage to your car, but for different causes. Collision pays when you hit something (another car, a guardrail). Comprehensive pays for almost everything else: theft, vandalism, fire, falling objects, floods, and animal strikes.

Do you need both?

If your car is financed or leased, yes. If it's paid off and older, weigh the combined cost against the car's value.