On this tab you can see a list of newsletters that the edited subscriber is subscribed to. More can be added by using the Add newsletters button, or existing ones can be removed by using the check-boxes and clicking Remove selected.
If the Send e-mail confirmation to the subscriber checkbox is checked when you click the OK button, the confirmation e-mail is sent to the edited subscriber saying that they have been subscribed to the newsletter.
More resources can be found at:
Page url: http://devnet.kentico.com/docs/5_5r2/contexthelp/index.html?subscriptions_tab.htm