In mathematics, a ratio is the comparison of two numbers or quantities which is an amount, measurement, or number.
For example, a ratio can be used to compare the number of shaded rectangles to the number of unshaded rectangles. In the first image, I provided an image of what this ratio would look like.
A proportion is a pair of ratios that are equal to each other.
If we're asked to determine if two ratios can form a proportion, we really want to see if the ratios are equal to each other. It's important to understand that if two ratios are equal, they form a proportion.