A part of the whole is a fraction. A whole can be divided into equal or in-equal parts. So, a part of an equally divided whole is a fraction. Fractions are represented one over the other.
For example: is a fraction.
1 is the numerator which is a part of the whole
2 is the denominator, which is the whole divided into 2 parts.
To make it easy:
One part of two parts is (That is, 1 part is the Numerator and the total number of parts is the Denominator)
Same as, One part of three parts is 1/3
Fraction, to Children can be introduced in a pictorial form to make an easy understanding.
A circle is divided into two parts. Number each part. The total number of parts is the denominator.
And a part of it or half (shaded part) of the total parts is the numerator.
Hence, the fraction has to be written as, (1 shaded part, out of 2 parts.)
This can be progressed by connecting the fractions with the common objects.