Explanation:
1. The coordinates that come first are x1 and y1 and the coordinates that come in second are y1 and y2.
(5,8) =x1 and y1
(12,3)=x2 and y2.
2. You have to plug the coordinates back into the formula.

d= (12-5) to the second +( 3-8)to the second
7 -5
You do it to the second power
49+10=59
and add a square root.
If you still need help let me know.