Let's start by looking at 6 (a).
Suppose you have half a pizza (consisting of 5 slices). Any one of those slices would represent the fraction you are looking for. You know that 1 is on top, so 5 (number of slices) must be on the bottom (5 in the square).
In the same way, (B) would be 1/6 (6 in the square).
Let me know if this makes sense or needs additional explaining!