submitting forms

I have created a plugin that post some information on the front page, this information only shows to unregistered users. I have another plugin that has a form that is called from the first plugin. This form will submit information to database to be stored. My question is, where am i suppose to be sending the information. Im using <form action”<?php echo $_SERVER[“REQUEST_URI”]; ?>”> and it sends me to the same page, which i want. Im not sure what im suppose to add to check that the page has been submitted and do i add it to the plugin code.