Fractions are parts of whole numbers.
You have probably heard of things like;
When describing part of a number we need to know how big that part is, and that is what the name of the fraction tells us - how big is that part.
For example, half means that the original thing was divided in half (into 2 equal pieces). Like this apple.
Or a third, which means that the original object was divided into 3 equal parts.
Like this wonton pastry:
Unit fractions simply mean that we are only interested in looking at ONE of those pieces.
To identify a shaded fraction, or what fraction something is of another, we need to know:
What fraction of the rectangle is shaded?
What fraction of the circle is shaded?