I cant access my database through php?

I am learning PHP and MySQL through tutorials, and now i am stucked at a point. In this i have to access my database using created php file, but after running error occurs,

SQL error: Access denied for user ‘’@‘localhost’ (using password: NO)

This means i am not providing username and password, but i dont know how do i provide it through php file ? Please help

Code :

******* form.php **********

<form method="post" action="user.php"> 
<p><b>User ID:</b> <input type="text" name="userid" /></p> 
<p><input type="submit" value="Search" /></p> 


********* User.php ************

     import_request_variables("pg", "form_"); 

     $db = mysql_connect("localhost:/export/mysql/mysql.sock"); 
     mysql_select_db("forum", $db); 
     $sql = "SELECT name, email" 
          . " FROM Users" 
          . " WHERE userid = '$form_userid'"; 
     $rows = mysql_query($sql, $db); 
     if(!$rows) { 
          $error = "SQL error: " . mysql_error(); 
     } elseif(mysql_num_rows($rows) == 0) { 
          $error = "No such user name found"; 
     } else { 
          $error = FALSE; 
          $user_name = mysql_result($rows, 0, 0); 
          $user_email = mysql_result($rows, 0, 1); 
<title>User information</title> 

      if($error) { 
           echo "<h1>Error accessing user information</h1>\
           echo "<p>$error</p>\
      } else { 
           echo "<h1>Information about $form_userid</h1>\
           echo "<p>User ID: <tt>$form_userid</tt></p>\
           echo "<p>Real name: $user_name</p>\
           echo "<p>E-mail address: <tt>$user_email</tt></p>\

The username and password are the second and third arguments to mysql_connect

$db = mysql_connect("localhost", "somuser", "somepassword");

Now it says,

SQL error: Access denied for user ‘admin’@‘localhost’ (using password: YES)

So what do i do now ???

try this
$link = mysql_connect(“localhost”,“root”,“”);