First you have to see how many times 8 can go into the number 13. If you look, 8 can only go into 13 one time, leaving 5 left over. 13-8 = 5 1 with 5 left over (Rather than writing 8/8, you must simplify to 1 to make it less redundant)
Since there is 5 left over from 8, you would then place it into the numerator place to get: 1 5/8