I believe you're asking for where the html file with the contents of: "It Works!" resides on your system?
If that (rather random guess) is correct: It depends on your distribution. You can either do: "locate index.html" (if you have updatedb setup properly) or find / -name "index.html" to most likely hunt it down. -OR- Let us know what distribution you have and how you installed your web server (package management, source, etc) and someone can tell you.