You make the denominators the same. The LCM of 6 and 8 is 48, so we are going to make the denominators 48.
6 x 8 = 48
8 x 6 = 48
So now we have 5/48 and 5/48. But because we changed the denominators, we need to change the nominators accordingly.
So for 5/48 (originally 5/6) we multiply 5 by 8, and for 5/48 (originally 5/8) we multiply 5 by 6.
5 x 8 = 40
5 x 6 = 30
So now we have 40/48 (originally 5/6) and 30/48 (originally 5/8).
5/6 is greater than 5/8
Hope this helps!