Alright kiddo, imagine you have two candy bars - one is twice as big as the other one. The relative difference between the two candy bars is the difference in size compared to one of the candy bars.
So, if the small candy bar is 1 inch and the big candy bar is 2 inches, then the relative difference is 100% because the big candy bar is twice as big as the small one.
If the big candy bar was 3 inches instead of 2, then the relative difference would be 200%, because the big candy bar is now three times as big as the small one.
The key thing to remember is that relative difference shows how different something is compared to something else, and it's usually expressed as a percentage.