In order to enter in edit mode, select a grid cell and start typing, "Click" or press the "F2" key. You can also navigate through the cells using the keyboard arrows or with the "Tab" and "Shift + Tab" key combinations. To cancel the cell editing, press the "Esc" key. To save the changes press the "Enter" key or select another Grid cell. Pressing the 'Space' key when a checkbox cell is selected will toggle the check state.