When in the mix down of a project - how would finally tweat the piece - i.e. - gilasenndro - cressandro - any other effects that can be used to even it out - to sound smoother. 
I’m not 100% sure what you mean, but I think that you may be looking for the “Compressor” effect: http://manual.audacityteam.org/manual/help/manual/man/compressor.html
Or perhaps you are looking for the Envelope tool (See here http://manual.audacityteam.org/help/manual/man/envelope_tool.html)