Please Help me I am thick!!!!

Hi

When I go onto New Instrument - it is letting me pick instruments from Groove Agent and Halion now BUT I am getting no sound. It comes up with “Track Instruments” and “Rack Instruments” - Track instruments I can choose from Groove agent etc but Rack instrument only has Prologue…

I have downloaded a couple of the freebies from the link - thanks - but not sure how I get to use them on cubase - ie they dont show on my VST instrument list???

Sorry I must be doing something stupid somewhere but need help!!

Thanks

Mark