<select name="cid">
<option value="0" selected>Категория не выбрана</option>

<?php
$res = mysql_query("SELECT id, name FROM news");
while ($row = mysql_fetch_assoc($res)) {
    echo '<option value="'.$row['id'].'">'.$row['name'].'</option>';
}
?>

</select>

id    cat_name
1     cat_name_1
2     cat_name_2   
3     cat_name_3

id    cid    product_name   
1     1      product_1_1
2     2      product_2_1
3     2      product_2_2
4     2      product_2_3
5     3      product_3_1
6     3      product_3_2

<?php 
$result = mysql_query ("SELECT id, name, discription FROM categories",$db);
$myrow = mysql_fetch_array($result);

do {
printf ("
<table width='740' border='0' align='center' cellpadding='0' cellspacing='0' class='katalog'>
  <tr>
    <td width='360' height='20' align='left' valign='top' class='bg_category'><div class='name_title'>  Категория: | <a href='view_categories.php?id=%s'> %s</a> | </div>
      </td>
      </tr>
  <tr>
    <td colspan='2'>%s</td>
  </tr>
  </table><br>",$myrow["id"], $myrow["name"], $myrow["discription"]);

}
while ($myrow = mysql_fetch_array($result)); 
?> 

<!--выводим с помощью ду вайл все из таблицы produkts где id = категории-->
<?php 
$result = mysql_query ("SELECT * FROM produkts WHERE categories = 1",$db);
$myrow = mysql_fetch_array($result);

do {
printf ("
%s - name
<br>
%s -categories
<br>
%s - meta_k
<br>
%s - meta_d
<br>
%s - diskription
<br>",$myrow["name"], $myrow["categories"], $myrow["meta_k"], $myrow["meta_d"], $myrow["diskription"]);
}
while ($myrow = mysql_fetch_array($result)); 
?> 

$id = (int)$_GET['id'];
$result = mysql_query ("SELECT * FROM produkts WHERE categories = $id", $db);

while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
...
}

$result = mysql_query ("SELECT * FROM categories");
while ($row = mysql_fetch_assoc($result)) {
    echo '<a href="site.ru://view_products.php?id=' . $row['category_id'] . '">' . $row['category_name'] . '</a><br />';
}

$id = (int)$_GET['id']; // принимаешь параметр
$result = mysql_query ("SELECT * FROM products WHERE cat_id = $id");
while ($row = mysql_fetch_assoc($result)) {
    echo $row['product_name'] . '<br />';
}

<?php 
$db=mysql_connect("localhost","admin-mebel","123",$db);
mysql_select_db ("irbit-mebel",$db);

$result = mysql_query ("SELECT * FROM categories");
while ($row = mysql_fetch_assoc($result)) {
    echo '<a href="view_products.php?id=$id' . $row['id'] . '">' . $row['name'] . '</a><br />';
}
?>

<?php 
$db=mysql_connect("localhost","admin-mebel","123",$db);
mysql_select_db ("irbit-mebel",$db);
$id = (int)$_GET['id']; // принимаешь параметр
$result = mysql_query ("SELECT * FROM produkts WHERE id = $id");
while ($row = mysql_fetch_assoc($result)) {
    echo $row['name'] . '<br />';
	}
?>

echo '<a href="view_products.php?id=$id' . $row['id'] . '">' . $row['name'] . '</a><br />';

//исправь на 

echo '<a href="view_products.php?id=' . $row['id'] . '">' . $row['name'] . '</a><br />';

$a = 'Билл Гейтс';
echo 'Привет, ' . $a . '. Ты балбес!';

Привет, Билл Гейтс. Ты балбес!

echo '<a href="view_products.php?id=$id' . $row['id'] . '">' . $row['name'] . '</a><br />';

$result = mysql_query ("SELECT * FROM produkts WHERE cat_id = 2");
while ($row = mysql_fetch_assoc($result)) {
    echo $row['name'] . '<br />';
}

<?php 
$id = (int)$_GET['id']; // принимаешь параметр
$result = mysql_query ("SELECT * FROM categories");
while ($row = mysql_fetch_assoc($result))

<table width='740' border='0' align='center' cellpadding='0' cellspacing='0' class='katalog'>
  <tr>
    <td width='360' height='20' align='left' valign='top' class='bg_category'><div class='name_title'>  Категория: |echo  '<a href="view_products.php?id=' . $row['id'] . '">'| </div>
      </td>
      </tr>
  <tr>
    <td colspan='2'>%s</td>
  </tr>
  </table><br>",$row["id"], $row["name"], $row["discription"]);

}

?> 

<?php 
$id = (int)$_GET['id']; // принимаешь параметр
$result = mysql_query ("SELECT * FROM categories");
while ($row = mysql_fetch_assoc($result))

<?php include ("connect.php");
if (isset ($_POST['title']))  {$name = $_POST['title'];}
if (isset ($_POST['name']))  {$name = $_POST['name'];}
if (isset ($_POST['categories']))  {$category = $_POST['categories'];}
if (isset ($_POST['meta_k']))  {$name = $_POST['meta_k'];}
if (isset ($_POST['meta_d']))  {$name = $_POST['meta_d'];}
if (isset ($_POST['discription']))  {$discription = $_POST['discription'];}
if (isset ($_POST['text']))  {$text = $_POST['text'];}

<?php 
if (isset($name) && isset($diskription) && isset($text))
{
/* пишем занести в БД */
$result = mysql_query ("INSERT INTO produkts (title,name,meta_k,meta_d,categories,diskription,text) VALUES ('$title','$name','$meta_k','$meta_d','$diskription','$text')");
if ($result == 'true') {echo "<p>Товар добавлен!</P>";}
else {echo "<p>Товар не добавлен, ошибка! Возможно проблемы на хостинге.</P>";}

}
else
{
echo "<p>Заполнены не все поля, продукт не добавлен.<br> Вернитесь назад и проверте все ли поля заполнены.</p>";
}
?>

<label>Выберетите категорию<br />
<select name="id">
<option value="0" selected>Категория не выбрана</option>
<?php
$res = mysql_query("SELECT id, name FROM categories");
while ($row = mysql_fetch_array($res)) {
    echo '<option value="'.$row['id'].'">'.$row['name'].'</option>';
}
?>
</select>