The default size of the grid is 20x20. You can press different letters to select different cell types to draw. By default all cells are empty.
S: start cell
F: finish cell
O: obstacle cell
E: empty cell
You can also press R to reset the grid to its initial state. After you have placed the start and finish cells and put the obstacles in place you can select an algorithm from the drop down menu. Click 'Start' button to run the algorithm. Click 'Stop' button to stop the algorithm.