HTML - Online Forms

Can someone please explain how forms work please.

I know how to set them up and send them to another file to be processed. How do i set up the file to process it?

Example:
My form:
Quote:
<form action="http://www.music-web.org/webmail2.php" method="post" name="webMailLogin">

<input type="hidden" name="submitted" value="y" />
<table border="0" cellpadding="0" cellspacing="0" width="100%" bgcolor="#FFFFFF">
<tr>
<td colspan="2"><img src="http://music-web.org/images/clearpixel.gif" width="1" height="12"></td>
</tr>
<tr>
<td class="black12" align="right"><b>Login:&nbsp;</b></td>
<td class="QuickDomainCheck"><input type="text" tabIndex="1" name=" login_name " size="20" value=""></td>
</tr>
<tr>
<td colspan="2"><img src="http://music-web.org/images/clearpixel.gif" width="1" height="12"></td>
</tr>
<tr>
<td class="black12" align="right"><b>Password:&nbsp;</b></td>
<td class="QuickDomainCheck"><input type="Password" tabIndex="2" name=" passwd " size="20" value=""> <input type="image" src="http://www.music-web.org/images/webmail/login.gif" align="absbottom" value=" Login " tabIndex="3" ></td>

</tr>
<tr>
<td colspan="2" align="left">
<BR><BR><div class="text" style=" color:000000; font-family:arial; font-size:10px; padding-left:124; padding-top:5">Login using your email address and password.</div>
</td>
<td class="black10"><br><br></td>
</tr>

</table>
</form>
It gets sent to:
Quote:
<script language="JavaScript" TYPE="text/javascript">
function submitMe()
{

loginName = ' I need the value of the form in here ';


//find @
atPos = loginName.indexOf("@");

//check >=1
if (atPos >= 1 )
{

//get the domain name length
domainLength = (loginName.length +1)

//get the domain name
domain = loginName.substring(atPos +1, domainLength );

//get the username
user = loginName.substring(0,atPos);

//set up the username to post to the mail form
document.implogin.loginuser.value = loginName;
document.implogin.imapuser.value = user;
document.implogin.pass.value = 'I need the value of the form in here ';
document.implogin.maildomain.value = domain ;
document.implogin.maildomain.realm = domain;
document.implogin.url.value = 'http://webmail.'+ domain + '/horde/login.php';document.implogin.action = 'http://webmail.'+ domain + '/horde/OWH_Logout.php';
document.implogin.submit();

}
else
{
alert('Please enter in your full email ie. someone@yourdomain.com');
}


}
</script>
I hope this isn't too confusing and someone can help.