How create a page in a plugin installation and get Url for use it?

I need to create a plug-in. This plug-in will allow a user to send it post data from an html form.

In the plug-in installation, how can I add a page based on my own template (compose by the API call with only PHP in) and get the URL of this new page for store it in the database like a parameter, permalink activate or not?

For example, a person enabled my plugin. After, she create a simple form and in the action attribute, she put this code [Url_to_Json]. Example :

<form action=”[Url_to_Json]”>…</form>

With an “Add_Filter” on “the_post” in my plug-in, I replace [Url_to_Json] with my URL page that containing the Json, create in the activation plug-in…