Custom Page for Plugin

After searching for minutes, I mean years, on google and the local search, I couldn’t seem to find the information I was looking for.

I am working writing my first plugin. It is a send to friend plugin. The plugin activates correctly, builds the required tables.

I’m not quite sure how to “use” the plugin. I have a page with a form on it that I want the user of the plugin to be able to link to. How would I go about doing this? What is this called?

To sum it up better, my plugin has a php file with a form on it. Once the plugin is installed how do I get users of the plugin to be able have their site users see the php file with the form on it/

Thanks.