Lists are used in campaigns to define the associated collaborators.
You can here create and edit your lists.
Lists can be 2 types: Combination and regular.
Combination lists - are lists that combine other lists. Ex:
Option "Add collaborators that appear in all of the specified lists" will add to the list all the collaborators that are associated to all of the specified lists.
While option "Add collaborators that appear at leas in one of the specified lists" will add collaborators that associated to at least one of the lists.
You can use these type of lists to associate collaborators with campaigns, but yo cannot use them inside of the campaign, meaning that you cannot add/remove collaborator to a combination list. To do that, you will have to add collaborator to one of the child lists (regular lists inside of the combination list).