Trouble loading PHP Class within the same project - php

Question

Someone could help me on the issue of referencing php files within the same project (calling classes) using "namespace","use" ( php v5.3 or higher) [My Screenshoot][http://i.imgur.com/6GC4UUK.png?1]
Zoho\
CRM\
Common\
-HttpClientInterface.php
Config\
Entities\
Exception\
Request\
Wrapper\
index.php
I've read about autoloading classes but I don't undersand very well..
Fatal error: Class 'Zoho\CRM\Common\HttpClientInterface' not found in C:\root\zohocrm-master\src\Zoho\CRM\index.php on line 73
<?php namespace Zoho\CRM;
use Zoho\CRM\Common\HttpClientInterface;
use Zoho\CRM\Common\FactoryInterface;
use Zoho\CRM\Request\HttpClient;
use Zoho\CRM\Request\Factory;
use Zoho\CRM\Wrapper\Element;
.
.
.
public function __construct($authtoken, HttpClientInterface $client =null , FactoryInterface $factory = null )
{
$this->authtoken = $authtoken;
// Only XML format is supported for the time being
$this->format = 'xml';
$this->client = new HttpClientInterface();
$this->factory = $factory ;
$this->module = "Leads";
return $this;
}
This is my class file :
<?php namespace Zoho\CRM\Common;
/**
* Common interface for Http clients
*
* #package Zoho\CRM\Common
* #version 1.0.0
*/
interface HttpClientInterface
{
/**
* Performs POST request.
*
* #param string $uri Direction to make the post
* #param string $postBody Post data
*/
public function post($uri, $postBody);
}