Some problems I have under the "Audio" menu

[asdfvideo123]

I have seen on some YT tutorial videos that you can add a second audio track by Audio->Second track.  But the problem is, I have only three things under "Audio" for me to choose -- Select Track, Save Audio, and Filters.
Select Track "allows" me to add a second track by enabling track 2, but it does nothing as no second track is played either in preview or in the rendered video.

I am using Avidemux 2.6.4 r8696 (32 bit) on Windows 7 , if that helps anything.
Any help will be very appreciated

EDIT:
Disabling Track 1 (The original audio track of the video) but leaving Track 2 (The background music I want to add) enabled makes the video plays the background music only but not the original audio track.  Is there any way to play both tracks at the same time?  I don't know why I cannot find the dual audio output in either Audio Output or the Output Format.

[mean]

you can add discting tracks (i.e. english, german, ...), and one can be played at any time

What it seems you want to do is merge 2 tracks (i.e. voice + backgroud noise)
You'll need an audio editor to do that (audacity or so)

The tutorial you are refering to is made for avidemux 2.5.xx