Revit automatically numbers each grid. To change the grid number, click the number, enter the new value, and press ENTER. You can use letters for grid line values. If you change the first grid number to a letter, all subsequent grid lines update appropriately.
As you draw grid lines, the heads and tails of the lines can align to one another. If grid lines are aligned and you select a line, a lock appears to indicate the alignment. If you move the grid extents, all aligned grid lines move with it.