You have started with Freshdesk and would like to add an email address to the portal so that when customers write to this address, all the emails would be converted into tickets. 

In order to process this, please navigate to Admin --> Support channels --> Email --> New Support Email and add this email address here. Once this is done, a "Forwarded To" address is generated which has to be set up in your mailbox. Kindly, navigate to this document which would help you convert all emails to tickets.