First, to make 3D shapes, open a new
document, any size, and choose a background. Now, create a new
layer. Then, go to filter>>render>>3D
transform.
Now, from the buttons on the left side,
select either the cylinder, cube, or sphere tool. I have
selected the cube tool. Draw several shapes in the middle of
your field of view.
Select
the same button as in the picture below. Press down on the
field of view while rotating your cubes, until they are no
longer transparent (until they look similar to below).
Now
click OK and you're done! Now you can colourize your cubes,
add shadows, text, etc! Here is my finished product:
