Email is one of the easiest ways in which your customers can reach you, so you need to make sure you put it up on your website and let all your customers know. You can use the support email address you received while you signed up for Freshdesk or you could integrate your existing support email with Freshdesk (Here's how to do it).
When a customer emails you a support query to your support email address, it will be created as a ticket in your helpdesk. You can send out an automated response to the customer using email notifications, giving them the public URL of the ticket and information about when they can expect a solution. Or you can just be personal and switch off notifications and send a response directly.
The email address of the customer who raised the query will become a contact on your helpdesk immediately. You can edit this new contact and add information like the customer's name and phone number as and when you get it.
The ticket created via email will be in the tickets tab with the source specified as email. You can just reply to it or perform actions like forwarding or adding notes. Your ticket replies will reach your customer through email. You can set up Knowledge base and Forums and encourage your customers to use your portal, or you can keep your helpdesk invisible make it a simple email conversation.