Square numbers look like this 2², 3², 4², 5² and so on...
When you square a number you multiply it by itself.
Take a look at the multiplication table below.
Example:
Two squared 2² = 2 x 2 = 4
Three squared 3² = 3 x 3 = 9
Four squared 4² = 4 x 4 = 16
Five squared 5² = 5 x 5 = 25