A simple question... on the bottom left you see the forest, and I'm want to see for making it so that as you move though you can see both backgrounds... However I know that the blue part of the forest needs to be transparent to allow you to see the 2nd background... But I can't figure out what needs to be done to enable this... How is it done?

When you import an image to use as a background in game maker, it gives you the option to make it transparent... this appears as a check box. The color of the pixel in the lower left corner is what becomes the transparent color in the background.