Consider you wanting to implement a simple game of checkers. There would be a rectangular game board and the player would able to move the pieces around according to a particular set of rules.
General good design principles suggest that we decouple the display of the game from it's data and logic.
That is, the display of the game board and the ability to click and move stuff around would be decoupled from the actual representation of a game board in memory. The data in memory doesn't know what displays it.