The exception provides everything you need to know:
please ensure both cURL and JSON modules are installed
cURL and JSON are PHP modules that need to be installed in your PHP environment as they Pusher PHP library depends on these to function.
If you could provide more information about your PHP runtime (PHP version and operating system) it may be possible to help you install these.
How to install cURL on Windows can be found here: How do I install cURL on Windows?
Official docs on the installation of cURL can be found here:
http://php.net/manual/en/curl.installation.php
Installing the JSON module for PHP5:
http://slaptijack.com/system-administration/lets-install-json-for-php-5/
Official docs here:
http://php.net/manual/en/json.installation.php
Generic information on installing PHP on Windows can be found here:
http://php.net/manual/en/install.pecl.windows.php