Need help with 'post link to facebook' button in php

hi guys,

thanks for the interest in my post…

i want to have a button at the bottom of my main page layout (main.php) of the facebook logo where visitors can click on it to submit the page as a link to facebook.

how can i set the button so it will post the link to whichever page the visitor is viewing i.e. when they are reading a news article the button action will post main.php?id=news and when they are on home, main.php?id=home.

thank you very much and i hope to hear form you.