For a "Mountain fold," fold the paper away from you, so that the fold is closer to you. For a "Valley fold," fold the paper towards you, so that the fold is farther from you.
I didn't create this one -- John Bringhurst did. It does in fact fly, despite its odd shape. The two flaps folded up in the final step are the wings, they should be perpendicular to the body, and point up. The heavy part is the front.
Hold the plane by its front, push forward, and release.
If the plane doesn't seem to be flying, try sharpening your creases.