To: bacsi
Actually files added to the timeline will all be saved as one audio file as a result, no matter whether you add your audio files one after another using one New Track line, or you apply them on different lines.
In case you mix them the first way, there will be no option to lay one track over another (see screenshot 1). In case you combine tracks using multiple lines (see screenshot 2), you will be able to overlay the tracks by moving them back and forth.
Regards