No matter Audacity is in repositories, I can’t install it. I downloaded audacity-minsrc-2.0.6. How can I install it from terminal?? 
A tarball is source code. So you can only install it after you extract the source code and compile it. See http://wiki.audacityteam.org/wiki/CompilingAudacityForBeginners.
You can usually install a precompiled package of Audacity from your distribution’s repository. Use your package manager to find a precompiled package of Audacity. Also see http://audacityteam.org/download/linux. What version of Linux do you use?
Gale