this extension requres Redis Magento Builtin cache enabled and php_redis php extension installed. The phpredis extension provides a native PHP API for communicating with the Redis key-value store.

#RHEL / CentOS
#Installation of the php-pecl-redis package, from the EPEL repository:

yum install php-pecl-redis

Nginx

fastcgi_param PHP_VALUE "auto_prepend_file=/var/www/html/magento/app/code/Mage/FPC/FPC.php";

/var/www/html/magento/app/ shuld be changet to your magento path

or

add it as a first line to app/bootstrap.php or pub/index.php

Also if you are using composer to install this stuff your path will be something like : ../vendor/mage/fpc/src/Mage/FPC.php

Installation into app folder is preferable. It is not a usless library. It is a part of your busines to keep your site FAST.

require "../app/code/Mage/FPC.php";

Also this extension will work without this aditional interactions (jsut install and forget) but it will be slower becouse it will load all Magento 2 via autoloader.

or do next:

composer require mage/fpc
bin/magento setup:upgrade
bin/magento fpc:deploy

FPC generation time is 0.000481128 second.