How to Replace Your Skies in Photoshop

In Photoshop, he shows you two similar mountain scenes, each with a different sky. To replace the unwanted sky, he layers the preferred sky image over the other photo, and aligns the two images. He creates a layer mask, then returns to the base layer, clicks Select, then Sky, and Photoshop singles out just the sky. He switches back to the layer mask, and paints black over that sky, erasing it. This technique reveals the preferred sky from Layer 2 and creates the new image.