Question about Unity 2D Toolkit

I'm not sure if this is the right place to ask about help with an extension so I apologize if this is the improper place. I'm having a simple issue. I just need to know how to use transparent sprites correctly. If you look below at the image I uploaded you'll see that the transparent part of my rocks don't show what is underneath it. In this case it should be grass. Also, when I make my tileset my house pieces seem to be randomly placed. I'm pretty sure this is a easy fix, but I seem to be having issues figuring it out.