If you're not sure what a file's format is, you can look at the extension at the end of the file name (for example .docx, .txt, or .jpg). On some computers, the extension may be hidden, and you may need to look at the icon to determine the file format.
Mobile apps
Desktop and laptop computers aren't the only devices that can run apps. You can also download apps for mobile devices like smartphones and tablet computers, which opens up a lot of new possibilities. Here are a few examples of mobile apps: