Well first off you need to know how you are going to view a news item? Is this going to have all news articles on one page and below each news article is a to post new comments? If so then each of these forms generated per news article should have the news ID in the form potentially as .
Example:
<p>News article 1.</p>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<input type="hidden" name="new_id" value="1"/>
<textarea name="comments"></textarea>
<input type="submit" name="submit" value="Post COmment"/>
</form>
<p>news article 2</p>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<input type="hidden" name="new_id" value="2"/>
<textarea name="comments"></textarea>
<input type="submit" name="submit" value="Post COmment"/>
</form>
Then on this page at the top you can check for whether or not user pressed submit button:
<?php
if(isset($_POST['submit'])){
//$_POST['new_id'] is news article id
//$_POST['comments'] is comments for this
//sql to store new_id = $_POST['new_id'] and comments = $_POST['comments']
{
Alternatively:
Lets say on your home page you have links to each news article and you retrieve them on subsequent page using $_GET. So index.php displays news and getNews.php is where news is displayed. You could want to on index.php generate a link to getNews.php?id=
THis way on getNews.php you know which news article to get using $_GET['id'] and you can easily post comments to this using a similar technique to above, take $_GET['id'] and toss it into your form on getNews.php as hidden field.
Caution: be careful and sanitize your $_GET variable before using it.
?>