I am new to a lot of server configurations and options. I want to add extra php libraries/extensions to my server. Where do I add them? (I am on a CENTOS 6.5 VPS)

For example, I want to add the phpseclib php extension:

Their website instructions are minimum:

Usage This library is written using the same conventions that libraries in the PHP Extension > and Application Repository (PEAR) used to be written in (current requirements break PHP4 compatibility). In particular, this library needs to be in your include_path:

    <?php
    set_include_path(get_include_path() . PATH_SEPARATOR . 'phpseclib');

    include('Net/SSH2.php');
    ?>

It tells me how to use it, but it doesn't tell me where to add the actual extension files. Should I added it under?

usr/local/lib ?

usr/local/lib/php ?

usr/local/lib/php/pear ?

Or can I add it under public_html? Also, my VPS has several users under /home/.. is that away to make the library available for only one user?