Question

use of a jack stand
always place a jack stand(s) and the jack fails to support the vehicle. the jack stand prevents the vehicle from damaging the person working on the vehicle from being injured.
check to ensure the floor is suitable to use a jack and stands. the floor should be level and firm; so the risk of the vehicle falling or sinking is minimal.
position the jack stand under a load bearing part of the chassis. neglecting this might cause the cup of the jack stand to damage the vehicle; as well as cause the vehicle to be unstable.
if the suitability of a jacking/support point is in question, consult the vehicle service information.
what is important when jacking up a vehicle?
check to ensure the floor is level and firm.
using the correct jacking/support points.
using a jack stand(s) to support the vehicle, when the vehicle is at the desired height.
check

Explanation:

The text clearly states that when jacking up a vehicle, it is crucial to check the floor is level and firm to minimize the risk of the vehicle falling or sinking. It also emphasizes using correct jacking/support points to avoid vehicle - damage and instability, and using jack stands to support the vehicle at the desired height in case the jack fails.

Answer:

Check to ensure the floor is level and firm, Using the correct jacking/support points, Using a jack stand(s) to support the vehicle, when the vehicle is at the desired height.