In the real world, there are not only whole numbers. E.g. bread can be cut into two halves and pizza into eight slices. To describe them we use fractions. They simply tell us how many parts of a whole we have.
Fractions show parts of whole numbers. Each fraction consists of a numerator and a denominator. The numerator is the top digit that represents how many equal parts the fraction contains. The denominator is the bottom digit that represents how many equal parts the whole is broken into:
We can also consider fractions as numbers on a number line. In order to represent $1/8$ on the number line, draw the number line from 0 to 1 . Now, divide the gap between 0 and 1 into eight equal parts (denominator=8). This represents fractions from $1/8$ to $8/8 (=1)$.