$servername = "ejemplo.es";
$username = "ramon";
$dbname = "bbdd";
$password = "loquesea";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
}

<?php

class Database
{
    private $_connection = null;

    public function __construct($host, $username, $password, $database)
    {
        // connect to database and store the connection for further use
    }

    public function doThisAndThat()
    {
        // do some fancy database stuff
    }

    public function __destruct()
    {
        // important for databases is to disconnect from them
    }
}

$db = new Database($host, $username, $password, $database);
$db->doThisAndThat();