GRANT ALL PRIVILEGES ON *.* TO 'root'@'%'
IDENTIFIED BY 'your_pass'
WITH GRANT OPTION;

sudo ufw allow 3306/tcp
sudo service ufw restart

[mysqld]
bind-address= your-server-ip-address
#skip-networking

<?php
$dbname = 'dbname';
$dbuser = 'db_user';
$dbpass = 'db_pass';
$dbhost = 'your-server-ip-address';

try {
   $connection = new PDO("mysql:host=$dbhost;dbname=$dbname", $dbuser,
   $dbpass);

 $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
   echo "Connected successfully";
 }
catch(PDOException $e)
   {
     echo "Connection failed: " . $e->getMessage();
   }