The square of a number is the number multiplied by itself. For example, two x two equals four, which is the square for that number. In Excel 2010/13 spreadsheets you can add squares of specified values together with the SUMSQ function.
As an example, enter the values 2 and 2 in a couple of Excel cells. Select a spreadsheet cell to add the SUMSQ function to. Press the fx button to open the Insert Function window.
Select the SUMSQ function from that window. That opens the window below where you should select both the numbers entered into the cells. Press the buttons beside the text boxes, and select the numbers.
Then Press the OK button to close the window. The function should return a value of eight as shown in the shot below. The square number of two is four, so the function adds four + four to give you a total of eight.
Alternatively, you can find the sum of two square numbers without entering any values in the spreadsheet cells. Select a cell to add the function to, and click in the formula bar. Enter =SUMSQ in the formula bar followed by brackets that include the two values. For example, you could enter =SUMSQ(2,2). Press Enter to add the function to selected cell.
This Excel function gives you a handy shortcut for summing square numbers. You can open this YouTube page  for further SUMSQ details.