Which OS have you really got. Yosemite started with 10.10.x
Audacity doesn’t support Yosemite yet.
However, it should’t be that bad. Are you trying to run Audacity from inside the dmg? You have to actually install Audacity for it to work.
https://forum.audacityteam.org/t/installation-do-not-run-audacity-from-the-dmg/31711/1
Koz