The URL (of the script to process the form data) should be whatever you want!!! E.g.
1. Suppose the form is in a file called "index.php" and you want it to process the form data itself, the syntax would be:
<form action="index.php" method=post>
2. Suppose the form is in "index.html" and the data is to be processed by a separate file "sender.php" which is in a child directory "process", the syntax would be
<form action="process/sender.php" method=post>
I.e. It all depends upon the name of the file containing the php script, and where it is located with respect to the file containing the form. Note: Relative paths are preferred because they work off-line for development as well as on-line live.