After unzipping you should have

README.txt - this file

fstar.jpg
Ionized.png

Move or copy these two files into the folder  Celestia\textures\medres folder
(on my computer the Celestia folder is in C:\Program Files )

wasp1 star.stc
wasp1 planet.ssc

Put these two files into a folder Celestia\extras\

Once you have done this, you can run Celestia and go to "Wasp1 star"