6. Scaling The Grid  Here we’ve zoomed in to take a closer look at the grid. On the right of the art board are three handles. The uppermost of these controls the Grid Cell Size. Adjusting this will help drawn elements to Snap To Grid, though there maybe times when you need to position freely. Perspective Grid has its own Snap to Grid option. 

7. Drawing In Perspective  By default in the upper left hand corner of the screen is the Active Plane Widget. Draw a rectangle then select the Perspective Selection Tool. Use the Perspective Selection Tool to reshape the rectangle, note how the rectangle conforms to the one plane of the Perspective Grid. Hover your cursor over the Active Plane Widget, make an alternative plane active. 

8. Changing Planes  Keyboard shortcuts now come in handy. Select the Rectangle Tool. Its icon looks different. It has arrows indicating on which plane a shape will be drawn. 1 is Left Grid, 2 is Horizontal Grid, 3 Right Grid and 4 allows you to draw without conforming to a grid. Toggle through these options, draw a top and side to complete your box.