We are going to skip ahead to saving for the Web, assuming that you’ve made whatever adjustments you require. Obviously, if you need to edit the image, do that first and continue with this step later.
Go to File / Save for Web/Devices and click. It is about half way down the drop down menu.
This process doesn’t change your original file at all. You are creating a new file. Once you complete this tutorial and return to your original image in Photoshop you’ll need to save that file if you’ve made any changes to it. It’s important to name your new image different than your original one. Often simply adding _web to the file name will work well. (example: filename_web.jpg)