In this Photoshop tutorial we're going to make a pyramid. Open a new image, 350 x 250 pixels.
Go to the menu and select: View / Show / Grid

 

Select: View / Snap (but only when there is no symbol in front of it):

 

Select View / Snap To / Grid (but only when there is no symbol in front of it):

Select Edit / Preferences / Guides, Grid & Slices and enter 1 Inch for gridline

or 25 mm if you use the metric system.

Go to the Tool Bar and select the Rectangle Tool or press the letter U on your keyboard. Now make sure that the option Paths is selected in the Options Bar:

 

Note: You can change the color of the shape by double clicking on the color box in the options bar:

 

Now activate the Move Tool in the Tool Bar.
Make sure that Show Bounding Box in the Options Bar is selected:

In Photoshop CS2 it's called Show Transform Controls.

 

We don't want to see only one side of the pyramid when we're done, so we're going to rotate the base shape.
Move your cursor close to one of the corner points until it changes into a double arrow and press and hold your left mouse button and rotate the shape until you have something like this:

 

Release the left mouse button and double click on the shape to finalize the rotation.

We're still looking at the base of the pyramid from a bird's view perspective, as if we're flying above it. We add perspective by pulling down the point marked with red...

...until we have something like this:

Double click on this shape to finalize the action and turn 'Show Bounding Box' off ('Show Transform Controls' if you use Photoshop CS2).

By only drawing the base we're able to draw the rest of the pyramid as soon as we know where to mark its top.
For that you need to remember the center point (X) of any of the virtual diagonals (look at the next image), either the center of line A-D or line B-C.
Once you have that center (X), then you know where to place the top (T), which should be somewhere along the vertical line going through X. Where exactly along this line? In reality it equals the distance between X and any of the corner points, but since we're dealing with perspective, things get a bit more complicated, so without getting involved in math, since that's not what we are here for, you just imagine the top above X, at a distance of about 2/3 of the length of for example line C-D.

Rotating the shape and changing its perspective hasn't moved the original center of our rectangular shape, so it will still be exactly on the vertical guide going through the middle of our shape, so keep that in mind when you mark the top in our next step (just let it snap to the guide that is party covered by the red arrow in my example)).

I hope that all this doesn't sound all too confusing and if it does, don't you worry; continue to the next page and things will become much clearer.