Grids can be useful when laying out your design freehand. To turn grids on, choose View>Grid or press Cmd+' [Single Quote] (Ctrl+'). Even more useful is the ability to turn on Snapping to the grid by pressing Cmd+Shift+' [Single Quote] (Ctrl+Shift+'). To adjust grid options, go to the preference menu and set frequency. (You have to have the Composition Window selected to use grids. Command+` toggles between the Composition Window and the Timeline. Command+Shift+` toggles between the Project Window and Comp Window.)