QUESTION html form with post method

[pewu]

Hello and sorry for the simple question. I am a newbie so ... Can anyone suggest me how to create my own form? I have code :

Code:

<form id="form" name="form_name" action="#" method="POST">
<input type=radio name="sth" value=1 >1 <br>
<input type=radio name="sth" value=2 >2 <br>
<input type=radio name="sth" value=3 >3 <br>
<input type=submit value="GO 1" onclick="document.getElementById('form').action='go1.php';" >
<input type=submit value="GO 2" onclick="document.getElementById('form').action='go2.php';" >
...

And how to create go1.php and go2.php files in GS ?
Where can I use '$_POST['sth']' in GS?
Do I have to create a plugin?
Any ideas, tutorials or manual guides ?

Thx