Ok I understand that but I made a simple drawing of a house. How do I create an alpha image to use in a 3D software app? Do I just use the magic wand and select everything but the house and make it black. The go back and use the magic wand to select the house and make it white. Then save image (tiff for example) and then use it in 3D app?

Or use the Brush and simply paint black to hide, and white to show through. Or use the Lasso, or use Paths, OR the Wand - and yes, Ctr+d to Deselect.

Again, show us the image that you're working on, and we can give you the best or most direct methods - until then, it's complete guesswork on our part - does it require feathering, are there somewhat translucent areas - we have NO clue unless we see it.
-Lew ;-)