To practice with the “Save for Web” tool, open an image in Photoshop; click “File>Open,” browse for the image on your computer, and click “Open.” For the purposes of this tutorial, a photo will work well, though any type of image will do. Resize your photo to a small size that you may use on a web site. To do this, click “Image>Image Size,” enter a new width in the “Pixel Dimensions” box (try 400) and click “OK.”