These are two different roles, but can be filled in by the same person (that is by the same email address): the Administrator is the actual owner of the list, the only person who can delete it, while the Moderator is responsible for supervising the behaviour of the subscribers, with the right to remove the email addresses that break the rules.

Both the administrator and the moderator, if selected, can manage the list, as far as their permissions will allow.
You need to specify an email address for each role, but while the first is requested when you create the list, the second must be added after the process has been completed.