function login( $user, $pass )
{
	if ( isset( $_POST['login'] ) )
	{
		$user = escape( $user );
		$pass = escape( $pass );
		
		if ( empty( $user ) )
		{
			$error = "Username field is empty!";
		}
		else if ( empty( $pass ) )
		{
			$error = "Password field is empty!";
		}
		else
		{
			$pass = md5( $pass );
			$fetch = mysql_query( "SELECT * FROM `user` WHERE `user` = '".$user."' AND `pass` = '".$pass."' LIMIT 1" ) or die ( mysql_error() );
			if ( mysql_num_rows( $fetch ) != 1 )
			{
				$error = "Username or password is incorrect!";
			}
			else
			{
				$got = mysql_fetch_array( $fetch );
				session_start();
				$_SESSION['id'] = $got['id'];
				header( "Location: home.php" );
			}
		}
	}
}

Simple Login Function

PHP