The GridDot command enables a grid of dots on the graph screen (you can disable it with the GridOff command). How fine or coarse the grid is depends on the Xscl and Yscl variables. Drawing the grid just involves plotting points all the points of the form (A×Xscl, B×Yscl) that are in the graphing window. The grid can be any colored defined by a color variable or value.
:GridDot BLUE //creates a grid of blue dots :GridDot 12 //creates a grid of black dots