On the ticket as an agent you can leave Public or Private notes.

Public notes will be visible to the ones who raised the ticket through the customer portal, however it will not send out email. Public notes will appear in light grey color. It should be used, if internal communication is needed without sending out an e-mail to the requestor!

Private notes will only be visible for the users internally using Freshdesk when they are on the ticket. These notes will appear with orange colored background

You can add a note in when you hit "Add note" on the top or bottom of the page. The button is located next to the reply button.

Once you had clicked the button, it will open up the textbox for the response.

You will have the option here to change the note type between private and public, add or remove contacts that should be notified.