Once you have downloaded your VST (.dll file), you will need to move the .dll file (for example, Gsnap.dll) into your Audacity VST plugins folder.
But how do you find that folder?
1) Click on your "C Drive" and look for "Program Files".
2) Click on "Program Files" then search for an "Audacity" folder.
3) Then click on "Audacity" and look for a "Plugins" folder.
4) Then click on "Plugins" and paste in your newly downloaded .dll file
Next, you have to get Audacity to search for this file. To do this:
1) Open Audacity
2) Click Edit
3) Scroll Down and click on Preferences
4) Click on Effects
5) Check the box that says "Rescan VST effects next time Audacity is started"
6) Restart Audacity