Editing data in the grid is dependent on the data type of the chosen column. In its simplest form, for text and numeric values, you can left-click or press the tab key to the required cell and type in the new value. When you move to another cell, values that have been edited but not yet saved are indicated by a different shade of background on the edited cells.
To save your changes click the Save button in the top left hand corner of the application, or use the Ctrl-S key combination. If you move away from the grid without saving your changes you will be prompted whether to save them or not.