Audacity

This evening I downloaded and installed Audacity on my MBP (10.6.8), seemingly without issues, but when I start it I get an error message "Critical Nyquist files could not be found. Nyquist effects will not work".

Have I done something wrong (in which case, what?) or not done something I should have done?

I have never seen that error. Where did you download Audacity? I have used it for years here. Could be a bad download. How did you install it, drop it in the Apps folder?

Check the last post in this thread.

http://forum.audacityteam.org/viewtopic.php?f=47&t=66553

OK, I removed Audacity and re-installed it from the same download. I'm now running it from within the Audacity folder and I no longer get that message. Thanks for the guidance.

Now, it seems that there are copious add-ins, plug-ins, etc. Which of these should I install? Bear in mind that I've never seen this software before and don't know what it can do.