After unzipping you should have

README.txt - this file

gstar.jpg
mercuryred.jpg
venussurface.jpg

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

kepler10.stc
kepler10bc.ssc

Put these two files into a folder Celestia\extras\

Once you have done this, you can run Celestia and go to "kepler10"