1 million is 100^3 (i.e. a cube 1 metre across, contains a million 1 cm cubes)

1 billion is 1000^3 (1 m cube contains a billion 1 mm cubes)

1 trillion is 10,000^3 (I can't visualize 0.1 mm, so increase size: the big cube is now 10 m on side, with 1 mm parts)

So the million and billion you could have on your desk made of parts that you can see and handle; the trillion is just a bit too big for that, you'd need a big room with a high ceiling.

Edit: and, of course, you can also see a million in 2D. A sheet of grid paper 1 m across, with 1mm grid squares. Or, more practically, try counting the pixels on a 720p monitor: 921600 pixels on that screen. Use checkerboard pattern.