You can use your mouse, of course, to navigate through a grid but there are other methods that are just as intuitive.
You can use your arrow keys on your keyboard up, down, left and right just as you would with Microsoft Excel. When you move through a grid in this manner, you will occasionally come to a cell that is editable. When you do, you can either type in the cell and edit the value, or you can continue to hit the arrow key and move past the editable cell without editing.
When navigating through a single row, you can also use your TAB key on your keyboard to move to the right, and SHIFT + TAB to move to the left. Again, if you come to a cell that is editable, you can choose to edit the cell and then tab (or shift + tab) to move out when you are done editing.