新聞財經娛樂♬資訊 News Economy

Wow, I tried to explain the issues, and for my effort I got the worst possible grade you can give to someone at EE?  The question requires a narrative answer.  Please take a look at the grading guidelines here.
http://www.experts-exchange.com/help/viewHelpPage.jsp?helpPageID=26

I'd like to continue to help, but I think you would be better off to get the SitePoint book and start there so that you can get some grip on the basics of the language.

Let's try to deconstruct this question...A form is an HTML construct that enables a client web page to make an HTTP request to a server.  The most common methods of request are GET and POST.  GET is used to "get" information when no changes are needed on the data model of the server.  POST is used to send information to the server when that information changes the data model of the server or the state of the client.   Examples of this include logging in, purchasing products, signing up for events, etc.  A POST request would be appropriate in the script you posted here because it attempts to set a cookie, and cookies are used to change the state of the client.

Will the script re-run?  That is anybody's guess.  The script tests to see if two data elements are not NULL (line 7).  If both are not NULL, the script will try setcookie() and then exit.  So depending on the data that the client entered, the script might re-run or might not re-run.  But in any case, the call to setcookie() will fail for the reasons outlined above.

Is this making sense to you?

Please, please give yourself some opportunity to learn PHP in a structured way, such as buying this book and working through the text and examples.  From this and your other questions it seems like you're floundering about and not really getting a good understanding of how the language works.  You can learn PHP, but not by reading other people's code without any understanding of the thought processes.  The SitePoint book will tell you what the author was thinking and how the code implements the ideas.
http://www.sitepoint.com/books/phpmysql4/

In the script above an echo precedes setcookie().  Cookies are part of the HTTP headers and all headers must come first, and be complete, before any browser output.  Echo creates browser output, so the setcookie() function fails.

The $_POST array is a superglobal variable, present in every scope and namespace.  It is empty if a POST-method request has not been made.  The script should test to see if $_POST is empty() before trying to use information from an empty variable.

The $_SESSION array is also a superglobal variable. It is (unfortunately) usable whether or not session_start() has completed successfully.  You use $_POST to collect external data from a POST-method request.  You use $_SESSION to store data that is originated in your script, when you want this data to be available to other pages of your web site.

You will find that your programming life is a lot easier if you add error_reporting(E_ALL) to the top of your scripts.  PHP makes a lot of assumptions and does so silently.  A raised error reporting level will help you find some of the silent errors (such as relying on undefined indexes in the $_POST array).

$-post is the way data is got from the form