The objective of the game is to move numbers around the grid until each 'line' that passes through the center has the same sum as all the others. There are two buttons: 'swap numbers' and 'check grid'. Select two numbers and click on 'swap numbers' to change their positions. Use the 'check grid' button once all the sums are identical.
Here is a video that demonstrates how to play the game.
To play this game, select the appropriate settings: