//you can call this file init.php which has all your connetion details
<?php
define('DB_HOST','localhost');
define('DB_USER','root');
define('DB_PASSWORD',''); #for security reasons :-)
define('DB_DATABASE','redwood_new');

$con = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);
if(!$con){
echo "Connection error...".mysqli_connect_error();
}else{
echo "Database connection success..";
}

//then call this before every file that requires it, like:
<?php
require "init.php";
....
....