I have a custom post type called newsletter. Once the newsletter is created I want to create a link to download the newsletter from the admin section (the newsletter post type is not accessible from the front end of the wordpress site). When the download link is clicked it will run a function in my plugin. The question is how do I register a url with wordpress that will do such a thing? I'm sure this is something pretty simple and I'm just missing it.
You want (probably)
Check the Codex for what the other parameters mean.