Draw a box primitive in Photoshop

This shows how to make a non-perspective box with parallel sides to be used for getting familiar with representing geometric shapes.

Make a new file

Mode = Grayscale

Make a grayscale file, 640x480 pixels.

Under View, turn on Show Grid and Snap

Background layer

Keep your white background layer locked.

Swatches layer

Make a new layer named swatches

Make 3 small boxes as swatches:

15% black [L = 90]

40% black [L = 70]

70% black [L = 40]

Box Layer

Make a new layer, call it Box.

Using black and the line tool of 1 pixel, set to fill pixels, draw your box. Be careful to close the lines [keep corners without spaces.]

[Make a duplicate layer of this and call it Box Stroke. This will make better outlines on your box.]

Back to Box Layer. Using the bucket and dropper, sample from your swatch layer and fill the box sides with your grays:

top face – light

front face – medium

side face– dark

Turn off Show Grid and Snap

Light source layer

Make a new layer above the box and name it Light source.

Draw a little sun with rays emanating towards the box.

The purpose of this is to get a good sense of your light source for positioning your cast shadow.

Cast Shadows layer

Make a new layer, drag it below the box layer and name it Cast Shadow.

Using the polygonal lasso tool, make a shape approximating the cast shadow.

Go select/feather 8-9 pixels.

Fill with 50% gray.

This image shows adding a specular level [white gradient] on the top, slightly gradating the sides, and applying a mask to gradate out the shadow:

A sphere or a cylinder can be made in a similar manner. Both use gradients. The sphere gradient is radial. Both have radiosity on the right sides. The sphere has 2 specular highlights, and the cylinder has a specular gradation on the top, and a vertical airbrush line on the left side.