So, absolute value is the distance from zero, and we measure distance using positive numbers unless we want net distance.
For example, if you back up 10 feet and walk forward 10 feet, you just moved 20 feet, right? We could ask for net distance, which would be 0 feet because you're back where you started, but not in this case.
Negative 100 and 100 are both 100 away from 0, which is why |-100| = |100| = 100. Make sense?
Now, how do we find out how far apart two things are? We subtract! How do we make sure our answer is positive? We take the absolute value. If one is 66 tall and the other is 63 tall, they are 3" apart, right? |66 - 63| = |63 - 66| = 3"
Who is taller? We aren't told that, so if we say h = the height difference between the two girls...
h = |s - j| or h = |j - s|
Hope this helps!