Hi , I am trying to mix a track that has been recorded(vocal & backing) and add harmonies to it , when i mix down , the recorded harmonies are to loud over the original recording. Any ideas please would be appreciated. 
Turn the volume (aka gain) down on the new tracks.
This is really basic stuff, you should run through a few tutorials. But here’s a relevant video:
http://www.guidesandtutorials.com/audacity-tracktools.html
The bit you want is about 50 seconds in.
Tks alatham, did not know about this link, was a big help & will be for future.
Cheers 