The basics is easy, as far as I understand:

They type something like http://yoursite/yourscript.php?did=x&clid=y&confno=z
in their browser, or whatever they use to send it (like an voice respons system).

Your webserver activates your script. Your scripts processes the parameters and makes the answer. Your short story doesn't tell the rules about how to construct the answer from the input (the transformation rules, but I assume there's a database involved somehow), nor how the username/password-combination fits in.

Once the script has the answer it sends it back in some format, like php-scripts use to do.

Why not ask "them" for some clarification?

Kees