according to google to ad a plug in to the effects you need to open the register effects dialogue box. But I can find no such thing on Audacity. How do you ad a plug in to the effects.
In the manual is a “Frequently Asked Questions” section: http://manual.audacityteam.org/o/man/faq.html
Many of the most common questions are answered there, including: http://manual.audacityteam.org/o/man/faq_installation_and_plug_ins.html#vst_install