# Get Started

In this chapter we are going to talk about the most common task: purchase of a product using [Paypal ExpressCheckout](https://www.paypal.com/webapps/mpp/express-checkout). We assume you already read basic [get it started](../../get-it-started). Here we just show you modifications you have to put to the files shown there.

### Installation

The preferred way to install the library is using [composer](http://getcomposer.org/). Run composer require to add dependencies to _composer.json_:

```bash
php composer.phar require payum/paypal-express-checkout-nvp php-http/guzzle7-adapter
```

### config.php

```php
<?php
//config.php

use Payum\Core\PayumBuilder;
use Payum\Core\Payum;

/** @var Payum $payum */
$payum = (new PayumBuilder())
    ->addGateway('gatewayName', [
        'factory' => 'paypal_express_checkout',
        'username'  => 'change it',
        'password'  => 'change it',
        'signature' => 'change it',
        'sandbox'   => true,
    ])

    ->getPayum()
;
```

### prepare.php

Here you have to modify the `gatewayName` value. Set it to `paypal_express_checkout`. The rest remain the same as described in basic [get it started](../../get-it-started) documentation.

***

### Supporting Payum

Payum is an MIT-licensed open source project with its ongoing development made possible entirely by the support of community and our customers. If you'd like to join them, please consider:

* [Become a sponsor](https://github.com/sponsors/Payum)
