如何连接到phpmyadmin数据库？

I'm trying to connect to a database in phpmyadmin. I'm new to the process and unsure how to connect to it.I'm using godaddy to host. I have this line of code:

$db = mysqli_connect("https://.....secureserver.net", "...", "....", "authenticationdb_");

I went to the table on phpmyadmin and copied the url, then copied the username (the first "...") and password (the second "...") that I used to login in to godaddy, and the name of the database is authenticationdb_.

This is not working and I'm not sure why. I was unsure if the username and password were the ones that I used to login in to godaddy but I don't know what else they would be since i accessed phpmyadmin thru godaddy.

<?php
$servername = "localhost";
$username = "username";  //your user name for php my admin if in local most probaly it will be "root"
$password = "";  //password probably it will be empty
$databasename = ""; //Your db nane
// Create connection
$conn = new mysqli($servername, $username, $password,$databasename);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 
echo "Connected successfully";
?>