This is a standard CPanel host with a slightly custom CPanel interface.
Follow the standard CPanel installation as shown in the tutorial video Installing on CPanel Hosting in the video library.
This host does not have email catch-all functionality. This means that incoming emailed subscriptions will only work if an email forwarder is defined in CPanel for each autoesponder to the arpReach email address you create during the installation process (normally firstname.lastname@example.org).
Local SMTP sending is not available on all HostGator plans.
Use the standard CPanel cron definition.
php-cli /path/to/your/public_html/a/a.php cli/auto
php-cli /home/mylogin/public_html/a/a.php cli/auto