The Mailing Lists are used to group recipients into different lists. Each recipient can be connected to zero or more lists and the connection also as a
Status, the status can be
Unsubscribed. When using "Double Opt-In" new recipients will have a
Pending connection to the Mailing List until the subscription is confirmed.
Actions-menu in the top right corner, you'll find the import-wizard that makes it easy to import recipients. You can either paste a comma or semicolon-separated list or recipients or upload a CSV-file.