When you save your email for the first time the message details overlay will ask for a message name and email subject.
The message name will only be displayed within your account to make the message easy to identify, whereas the email subject is what will display in the recipients inbox as a teaser to prompt the recipient to open the email. (eg. June's Special Offers, or June's Newsletter, etc.)
Full message details can be accessed and edited from the drag and drop editor by clicking the 'Details' button on the right.
Here on the 'General' tab you can change the email subject or message name, you can also set up or edit the sender details as required.
The 'Sender Details' tab is used to update the details of the company sending the message. (this information appears at the footer of your message)
The 'Footer Links' tab is where you set up your unsubscribe or update profile link to display in the footer of your message