Lets say, we want to calculate the square of 39. The entire steps are illustrated in the following figure.
Step 1: On 25, given number 39 is 14 more. This is the 1st part of the answer.
Step 2: On 50, given number 39 is 11 less. Find the square of 11, the result is 1/21. We need to have only two digit number. If it is a 3- digit number left most digit is added to 1st part. The 2- digit number (21) is the 2nd part of the answer.
The final answer is 1521
One more Example: