You would
1. setup an email account (with either pop or imap connection capability).
2. configure the email address in OSTicket.
note: see http://osticket.com/wiki/Email_Settings(http://osticket.com/wiki/Email_Settings)
3. setup a cron or windows taskscheduler to run cron.php
note: see http://osticket.com/wiki/POP3/IMAP_Settings(http://osticket.com/wiki/POP3/IMAP_Settings)