Where things can get tricky is when you need to save the file in a different format. The most commonly used file formats are explained in my article, Which Graphics File Format Is Best To Use When?
If you're saving an image intended for the Web, it's best to use the Save for Web command (Alt-Shift-Ctrl-S on Windows or Option-Shift-Command-S on Mac). Photoshop's Save for Web command is specially designed for saving Web images, which you generally want to keep as small in file size as possible. Save for Web allows you to adjust various settings and save your images out to several Web-friendly formats. When saving your class assignments for these lessons, get in the habit of using the Save for Web command since your assignments will be posted to the forum.
