Li - To understand square numbers 

Today we are going to revise square numbers.

A square number is the result of multiplying an integer (not a fraction) by itself.

Example: 4 × 4 = 16, so 16 is a square number.

Here are the first few square numbers:
0 (=0×0)
1 (=1×1)
4 (=2×2)
9 (=3×3)
16 (=4×4)
25 (=5×5)

This square number song may help you. 

https://www.youtube.com/watch?v=8tZVIoj50ng