lol, well basically, what you would do is add an alpha layer by going to some tab, I think its the layers tab, then transparency, then add alpha layer. If i'm wrong, don't hold it against me. After that, all you have to do is highlight the area you wish to make transparent, and press the delete button on your keyboard (not to be confused w/ the backspace button). Thar u go ^.^
I myself still haven't worked out the semi-transparencies yet. I know there's a way, I just don't know how
