Issue with third party Google Analytics sdk - php

Question

I have code which works above the php 5
its actually GA Library, here is its github project.
I have cloned the project theiconic/php-ga-measurement-protocol
Since I am new to PHP, I have no idea where to put this code, Please help me here this project should be installed via composer via code
{
"require": {
"theiconic/php-ga-measurement-protocol": "^2.0"
}
}
After this step I need to create a file something.php and I need to put the code below, I am having problem on locating autoload.php on my server, Please look at the code below to understand what i am saying.
<?php
//grab the data that Calendly sent in the webhook and store it in a variable called $objCalendlySubmission...
$objCalendlySubmission = json_decode(file_get_contents('php://input'));
//We've passed the Google client_id in Calendly's placeholder for utm_term. Feel free to pass it differently, this is just an example
if(property_exists($objCalendlySubmission->payload->tracking, 'utm_term') && !empty($objCalendlySubmission->payload->tracking->utm_term)) {
$strPageViewed = 'calendly_conversion.html'; // We use different page names depending on what type of event was scheduled via Calendly
sendGoogleAnalyticsPageView($objCalendlySubmission->payload->tracking->utm_term, $strPageViewed);
}
function sendGoogleAnalyticsPageView($strGAClientId, $strURL) {
require_once '/path_to_composer/composer/vendor/autoload.php'; //loads the PHP library for the "Google Analytics Measurement Protocol” **I dont know where is it located exactly on my xampp server, Please guide me here**
$analytics = new TheIconic\Tracking\GoogleAnalytics\Analytics(true); //you may have to adjust this path based on your setup **please help me here**
$analytics
->setProtocolVersion('1')
->setTrackingId('YOUR-GA-UA-ID-GOES-HERE')
->setClientId($strGAClientId)
->setDocumentLocationUrl($strURL);
$analytics->sendPageview();
}
?>
In the above code towards middle line
require_once '/path_to_composer/composer/vendor/autoload.php'; //loads the PHP library for the "Google Analytics Measurement Protocol”
I dont know where is it located exactly on my xampp server, Please guide me here
$analytics = new TheIconic\Tracking\GoogleAnalytics\Analytics(true); //you may have to adjust this path based on your setup
Here is the image of Project folder
Project structure Part 2