// connect to database
	  $con = mysql_connect('localhost', 'root', '');
	  if (!$con) {
    	die('Could not connect: ' . mysql_error());
		echo 'Connected successfully';

	   $db_selected = mysql_select_db("template", $con);

	   if (!$db_selected)
  		die ("Can't use template : " . mysql_error());

	  // cek login
	  //undefined index: login
if (isset($_SESSION['login'])){
		echo "Anda tidak berhak mengakses halaman ini.";

	if (isset($_REQUEST['simpan'])){
		$kategori = mysql_real_escape_string($_REQUEST['kategori']);
		$id = $_REQUEST['id'];
		if (empty($id))
			$sqlstr = "INSERT INTO kategori_berita VALUES('".$kategori."')"  or die(mysql_error());
			$sqlstr = "UPDATE kategori_berita SET kategori = '".$kategori."' WHERE id =".$id;

These are the errors:

Connected successfully
Notice: Undefined index: kategori in C:\xampp\htdocs\php_template2\category_manager.php on line 97
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '=
Notice: Undefined variable: id in C:\xampp\htdocs\php_templa' at line 1

Line 97: $kategori = mysql_real_escape_string($_REQUEST);

What's wrong with these errors: I am trying to save information and would like to see it in table, yet the error appears and the saved information does not appears on the table.

There is no need to mention the values like ".$kategori." You just declare it as
mysql_query(insert into kategori_berita vaules('$$kategori'); if it is a string if not so just remove quotes.
And you didn't used query so the server will not understand which query should be executed please try the above syntax.

I suppose you are misspelled the form fields "kategori","id".
Check out your previous page for correct spelling.

It is clear , if you post the previous page code.

I wonder why in my category box is written:

<br /><b>Notice</b>: Undefined variable: kategori in <b>C:\xampp\htdocs\php_template2\category_manager.php</b> on line <b>122</b><br />
Kategory [_______________]

line 122: <input name="kategori" type="text" id="kategori" value="<?php echo $kategori;?>"/>

This has been described in your other post. $_REQUEST['kategori'] may not have a value, use isset() . Also, $_REQUEST is deprecated, use $_GET

try using

mysql_query(insert into kategori_berita vaules('$$kategori');