If you don't make your props transparent they won't work. It is easy and I have seen some people make it so hard. It took me a while to figure out how to make my white images stay white and not clear. To help you avoid that mistake I will tell you in the easiset way I can.
Transpanacy is the kae to being able to layer. Without using it, you will get a white square around your image that will block out what is under the item. And you can't just use white all the time, unless you don't plan on using anything with white in it. That is not good. I tried and some things just look better with white, if you know what I mean. I use paint, it varies by programs.

Click that and find Tranparancy. Mark the box, and click select color. Only use a color that is NOT in your image or else that color will turn out clear. I like to use the bright green.

Now you have to flood fill around you image the same color as you chose for your tranparent color. And, save. That's it you're done.

Yes, you will see the background color whie in paint. But, click open, and look at your files in a thumbnail view, you only see the image; Right? Great, that means you did it correctly. If you see the background color then you didn't flood fill with the correct color. Remember... the transparent color and the background color have to be the same.

Some other great transparency tutorials will be found below.