Authorities are a helpful way of providing data catalogers with a list of controlled vocabularies. This helps ensure data consistency across a collection. Authorities are created in the Collection Manager by designating a field group as an Authority.
If you have permission to makes changes to an authority you'll see the "Manage Authorities" button next to the "New Record" button in the Library. When you mouse over the button you'll see the list of available authorities. In the example below there are 6 different authorities within this collection.
When you select an authority you'll be taken the a list view wherein all available data values for that specific authority are listed.
With the right permissions you can create new authorities, and upload a .csv list of authorities. Catalogers would then easily pick from the list of available data. Authorities are managed in the Library, and permission for managing them in the Administrator.