This illustration is meant to help you picture how the multiplication of fractions works. One-third of one-seventh is one-twenty-first.
Recall that when we multiply 1/3 * 6 we get an answer of 2. So, it stands to reason that 1/3 of 1/7 will be a fraction smaller than 1/7.
Here's another example for you to study:
Now you get to try a few for yourself.