To save your Audacity project, which is an .aup3 project, select File > Save > Save Project As. As you work on your project, you should save it often in the event of a computer malfunction.

An .aup3 file is not universally accessible, you must have Audacity to be able to access it. Therefore, we must also export our final project as an .mp3. To do so, go: File > Export > Export as MP3.