PDO -> The PHP Database Object

The PDO represents a connection between PHP and the Database Server.

Given the word object  in the title, we know that to use PDO, we need to instantiate it first.

From the PHP manual , I got :

public PDO::__construct ( string $dsn [, string $username [, string $password [, array $options ]]] )

or you can use

$pdo = new PDO(string $dsn [, string $username [, string $password [, array $options ]]) ;

The PHP manual says that DSN  (Data Source Name) contains the information required to connect to a database.

In general, a DSN consists of the PDO driver name, followed by a colon, followed by the PDO driver-specific connection syntax

I use mysql , so in my case, it will be 

"mysql:host=$databasehost;dbname=$databasename"

The username and password are clear.

Options :A key=>value array of driver-specific connection options.
       Ref :https://php.net/manual/en/ref.pdo-mysql.php