If this doesn't happen make sure you typed in the script correctly. We want to compress a spring. Where the spring and plane meet. Give it a go, Leave the spring squashed on the plane as in the last example and move the plane up. The spring should also move up.
Lets start with lines of code and what they do.
Enter the exact name of the object. This stops the spring from going under the plane. But if the plane moved or we upsized our spring it wouldn't work. That is why in Step 3 we scaled the spring into a default size of a 2x2x2 grid. Just substitute numbers to variables to understand the code.