It is always a good idea to save your project (i.e., use the Save command) frequently as you work, in order to protect your project from data loss in the event of a computer crash or other system failure.
Use the Save command (File>Save or press the CTRL+S keyboard shortcut) to save the active project file with its current name and to its current location on your system. When you use the Save option for the first time, the Save Current Document As dialog box appears to allow you to name your project file, choose a directory location for your saved file, and set other project file options. (For more information, see Save Current Document As Dialog Box.)
You can use the Save As command to make a copy of the active project to modify or experiment with, but at no risk of harming the last-saved version of the original project file. When you use the Save As command, the Save Current Document As dialog box appears to allow you to rename the project file, choose a new directory location for the saved file, and set other project file options.