In abstract form, the result of dividing $\frac{a}{b}$ by $\frac{c}{d}$ is $\frac{a \cdot d}{b \cdot c}$. Another way of saying that is that we take the second fraction, $\frac{c}{d}$, and "flip it" to get $\frac{d}{c}$ [edits must be at least 6 characters, but here it's just one and it's an important one];; then we multiply the first fraction by the upside-down second fraction. In our example, we have:
I couldn't understand that "Suppose you want to measure six cups of flour, and all you have is a 1/2 cup scoop. How many scoops do you need?"