Question

keep the vehicle from moving by applying the park brake and chock the wheels that remain on the ground. if you are working on a vehicle with an automatic transmission, put the gear selector in the park position.

1. jack up the vehicle using a jack

put the jack under the correct lifting point of the vehicle, this information can be found in the vehicle owners or manufacturer service manual. avoid the weak parts of the vehicle body, such as the floor pan, radiator support and suspension members; as the jack or jack stands can penetrate or damage these parts!

1. use jack stands to support the load

place the jack stand under the correct lifting/supporting points of the vehicle (consult the vehicles owners or shop manual), slowly lower the jack until the jack stand fully supports the weight.
repeat step 5 and 6 for the other jack stands

1. check the stability of the vehicle

check the stability of the vehicle by gently rocking vehicle, the vehicle should have no significant movement; otherwise the vehicle is not securely supported by the jack stands.

1. remove the jack stands

when youre finished with your work, jack up the vehicle using a jack, remove the jack stands and gently lower the jack until the vehicle rests on the ground.
in preparation to jack a vehicle, why should you park the vehicle on a solid, level, smooth surface?
the vehicle may fall off the stands or roll away if not parked on a level surface.
the wheels of the floor jack need to roll easily as you raise and lower the vehicle.
the jack and or stands may sink into soft dirt or hot asphalt.

Explanation:

Parking on a solid, level, smooth surface is crucial. If on an uneven surface, the vehicle may fall off stands or roll away. Soft dirt or hot asphalt can cause jack and stands to sink. Also, for the proper functioning of the floor - jack, its wheels need to roll easily which is facilitated by a smooth surface.

Answer:

The vehicle may fall off the stands or roll away if not parked on a level surface; The wheels of the floor jack need to roll easily as you raise and lower the vehicle; The jack and or stands may sink into soft dirt or hot asphalt.