When you do this

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This is a valid (though not all that efficient) use of PHP. But when you attempt to use header(), you will always get that error because the very first line above - "" is page output. The server sends a content type header. So when you try to print a location header, it's too late, "headers already sent."

As for this,

Close. When you post a form, it posts data to the server. That data, for form method="post", is present in the PHP $_POST variable. So what it's saying is "if someone has posted this form, 'do something', otherwise display the form."

"Add it" is another whole topic. You have to cleanse the data, and also check to see if it already exists in the database, THEN add it. All that goes inside the first "if," but to be useful, we'd need to change our logic a little. If there's an error, we'd want to display the form.

- if the form hasn't been submitted, it displays the form. - if someone submits the form, -- Check the data. If errors, --- display form with errors -- if no errors, --- Store the data in the database --- Display confirmation message

There are a million and a half ways to do this, this is not the "best" solution but don't want to lose you in the details. :-)