Audacity is free, open source audio editing software that allows users to record audio files, edit them by cutting, copying, and pasting sections, and apply effects like changing speed or pitch. It can be used to record a voiceover and then import the audio file into other programs like websites, PowerPoint presentations, or movies. The tutorial explains how to record new audio, import existing audio files, do basic edits, add special effects, and export the final audio file so it can be used in other projects.