There are a few things you need to do in order to make clouds in Photoshop. First, create a new layer and name it Cloud. Next, select the Cloud layer and drag it into the bottom left corner of the canvas. Finally, select the Gradient tool and click on the black line at the bottom of the palette. Choose a dark blue color and drag it up towards the top of the Cloud layer. Now, use the Gradient tool to change how dark blue it becomes on top of Cloud. You can also use this same gradient tool to change how light blue or green it becomes on top of Cloud. Once you have made your clouds, save them as a file and close Photoshop.