An isosceles triangle has 2 sides that are equal.
I plotted these points. See attached screenshot.
The first side's distance is 5. You can just count those units along the x axis. (0,0) and (5,0) share the same y coordinate, so the difference in x coordinates is 5-0 = 5.
The next sides's distance is also 5. You can count that distance on the coordinate plane. (5,5) and (5,0) share the same x coordinate, so the difference in y coordinates is 5-0 = 5.
These two sides make a right triangle and are equal length. This is an isosceles right triangle.