The Gendex section includes a single property, Create GENDEX File. When Create GENDEX File is checked, GedSite creates a file in the format used by the GenDex Network, a genealogical index that combines entries from multiple sites on the web.
The GENDEX file is named "gendex.txt" and written to the "up" subfolder of the Output (-o) folder. Copy this file to your web site host when you copy the other files there. The full URL of the file will depend on the base URL for your site, but it will end with /up/gendex.txt, for example:
http://www.example.com/up/gendex.txt
If you change the number of people per page and republish your site, that will invalidate entries in prior versions of your gendex file and so you must submit an updated version to the GenDex Network site.