Option to add background sound to existing mp3 file sound

I am new to Audacity, I found that Audacity 2.0.4 are very useful to edit sound. I am working on a project that needed to add background of a audio sound. Is there an option that allow to do such thing? Thanks in advance


I think this little tutorial will provide all of the information that you need: http://manual.audacityteam.org/o/man/tutorial_mixing_a_narration_with_background_music.html

Thanks Steve,
I go through the tutorial and could not find the option for what I needed. Maybe I didn’t post my question clearly. What I really wanted to do is to able to to mix track A “back ground noise track” through out track B “original soundtrack” to make track B with back ground noise of track A. is there such option in Audacity 2.0.4? thanks again.