Send Automatic Order Confirmation text message to Customer's mobile number

Hi there,
I’m trying to integrate API which I’ve got from Textlocal.in (SMS gateway )
But i don’t know on which page i will have to put it ?
I want message to be sent on customers mobile number whenever places an order.
Below is the API,

<?php
    	// Textlocal account details
    	$username = '[email protected]';
    	$hash = 'Your API hash';

    	// Message details
    	$numbers = array(918123456789, 918987654321);
    	$sender = urlencode('TXTLCL');
    	$message = rawurlencode('This is your message');

    	$numbers = implode(',', $numbers);

    	// Prepare data for POST request
    	$data = array('username' => $username, 'hash' => $hash, 'numbers' => $numbers, "sender" => $sender, "message" => $message);

    	// Send the POST request with cURL
    	$ch = curl_init('https://api.textlocal.in/send/');
    	curl_setopt($ch, CURLOPT_POST, true);
    	curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
    	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    	$response = curl_exec($ch);
    	curl_close($ch);

    	// Process your response here
    	echo $response;
    ?>

What changes i will have to make in order to get working perfectly. Need suggestions.

Thank you!