There is not much to document however, even though a sentence would be sufficient, then that should be provided.
post to the url %url%, with user_email = %user_email% and user_pass = %user_pass% and url = <the_url>
To demonstrate, the command line curl could be used in this way
/usr/bin/curl -X POST -F "user_email=%user_email%" -F "user_pass=%user_pass%" -F "url=http://www.google.com/search?client=ubuntu&channel=fs&q=url+compression+script+php&ie=utf-8&oe=utf-8" "%url%"