通过PHP集成Paypal Express Checkout

I am PHP developer, have a homepage where I want to integrate paypal express checkout. First I want to sell digital goods and later on also non digital goods like postcards etc.. I already have created the sandbox accounts and credentials. But I don't know the next step now.

I found following link:

http://paypal.github.io/#merchant

If I click on the PHP tab there is mentioned:

Without composer

curl https://raw.github.com/paypal/merchant-sdk-php/stable-php5.3/samples/install.php | php

Since I not use composer it seems to be the correct step for me, but what does this command do?

Do I need to download the SDK (provided in the Links section of the same page) first and the run this command?

I used this site to initiate with paypal http://www.phpkode.com/scripts/item/paypal-buy-now-and-ipn-classes/

Hope it helps