Hi Danielle
I hope I'm not causing offence but presumably you are not proposing to alter code on a live Moodle site and I also assume that you realise that there are usually multiple files involved in displaying pages in Moodle?
I would suggest that you download a copy of the Moodle source code and set up a test server on your chosen system if you haven't already done so.
You might also give consideration to whether or not modifications to code are really required, perhaps all you need to do is edit something that appears on an existing page?
Perhaps you could more clearly describe what it is you want to achieve?
Best
Richard