distance = speed * time
Or if your talking about this one,
D=√(x2−x1)2+(y2−y1)2
Then explanation below -
You just have to have two coordinates and the format of the coordinates (x, y).
So basically you take your two coordinates (x, y)1 and (x, y)2 and label the x of the first coordinate x1 and the x of the second coordinate x2. Same for the y1 and y2, then substitute for the variables, times them by 2, add them and find the root of that number you get.
Simple, hopefully this isn't too confusing :)