Audacity is a free software, cross-platform digital audio editor and recording application. It is available for Windows, Mac-OS-X, Linux and BSD. wikipedia.org

"Narration is the act of telling a story, usually in some kind of chronological order."

Voice-over is a production technique where a voice, that is not part of the narrative (non-diegetic), is used in a radio, television production, filmmaking or other medium.

Voice acting is the art of providing voices for animated characters (including those in feature films, television programs, animated short films, and video games) and radio and audio dramas and comedy, as well as doing voice-overs in radio and television commercials, audio dramas, dubbed foreign

Voice-over is a production technique where a voice, that is not part of the narrative (non-diegetic), is used in a radio, television production, filmmaking or other medium.

Audio editing is the process of taking recorded sound and changing it directly on the recording medium (analog) or in RAM (digital). wikipedia.org