The Newsletter Subscriber screen is split into three sections: the text included with the automatic emails, a place to enter new email address to add to the subscriber list and a list of current subscribers. See the example below.

Newsletter Email Text
By default, your subscribers will see the following information when you add a new issue to the group.

You can add custom text to this message using the Newsletter Email Text box at the top of the page. Consider adding information about the issue, its contents or a special event in this section. As shown in the above example, subscribers can unsubscribe to your newsletter at any time.
Enter New Email Addresses
The second section of the Newsletter Subscriber screen allows you to enter email addresses to your subscriber list. You can add as many as you want. If the subscriber is already in the Site Builder system, their demographics will be visible to you once they have been added.
Current Subscribers
The bottom portion of the page contains a list of all email addresses that are subscribed to your newsletter. Each email will be linked to a screen showing the demographics, if any, of the subscriber. On the demographics screen, you can edit the email or other information of the individual subscribing to your newsletter.
If you do edit a subscriber's information, you only need to do it in one group, even if the person is subscribed to multiple groups.
You can also look at a list of all subscribers in this section and delete any that need to be removed. To delete a subscriber, check the box next to the corresponding email address and click "Update Inforamtion" on the top right.
Email Subscribers

The top right action box features a button that says "Email Subscribers." Click this if you want to send a message to all of your subscribers without a newsletter or document. This is useful for announcing special events or highlighting something that may have been omitted from an earlier newsletter or document.