dont understand db corction

I downloaded this code but i dont understand and edit.

please help me.

I would like to know that is $host and $useame.

If i get a public server how do I change it

<?php
class Database
{

    private $host = "localhost";
    private $db_name = "test";
    private $useame = "root";
    private $password = "";
    public $co;

    public function dbCoection()
    {

        $this->co = null;    
        try
        {
            $this->co = new PDO("mysql:host=" . $this->host . ";dbname=" . $this->db_name, $this->useame, $this->password);
            $this->co->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);   
        }
        catch(PDOException $exception)
        {
            echo "Coection error: " . $exception->getMessage();
        }

        retu $this->co;
    }
}
?>