Dekisugi on "What to put in the action parameter of the form tag in the plugin?"

Hi

I don't understand how wp plugin handle html form. Say, I develop a wp plugin that has a setting page which uses HTML form to handle input.

<FORM action="" method="post">

What to put in the action parameter? Should it be blank or the filename of the plugin php file?

I saw some sample code. They put in "options.php". It made me even more puzzled because I have no idea where is that options.php file.

Please help me understand.

Thanks a lot!
Narin