Final answer:
When parking downhill with a manual transmission, put the car in first gear. For uphill, use reverse gear. With an automatic transmission, use the parking brake.
Step-by-step explanation:
When parking downhill with a manual transmission, you should put the car in first gear. This will give you more control over the car and prevent it from rolling downhill.
When parking uphill with a manual transmission, you should put the car in reverse gear. This will help prevent the car from rolling backwards since reverse gear has a higher gear ratio and provides more resistance when the car is stationary. If you have an automatic transmission, you should use the parking brake to secure the car in both uphill and downhill situations. This will prevent the car from moving.