I'd rename the text file you download from "Monster Counting Game 1.2.txt" to "monstercounting.txt"
After that, put the script inside your npc/ folder. Probably inside npc/custom/
Then inside your same npc/ folder, look for the file called scripts_custom.conf and add a line to it saying
npc: npc/custom/monstercounting.txt
Or whatever you ended up naming the text file.
Once that's done all you need to do is log in as a GM with sufficient powers, and type in @reloadscript and the script will be loaded onto the server.
Or you can restart the server as well, either works.