Stacking platforms

I am completely baffled by Blender. I am trying to create one platform 8" x 36" x 72" on top of another platform. How do I offset one platform by 8" in the z direction so that it stacks on top of the other?

Just add your values in the coordinates panel:

Also you can have a look on array modifier to create platforms.

Thanks, unfortunately, it took me a long time to realize that ā€œnā€ brings up the coordinates panel. Blender is very opaque to me as a newbie. There are all sorts of secret commands which are non intuitive and which are essential to use blender. But thanks for taking time to reply to my question. It helped.