What are metadata sets?
A metadata set is a collection of metadata fields and properties that control how those fields behave in user interaction. If you've used FotoWeb 7.0 in the past, you'll need to understand that metadata sets are similar to FotoWeb 7.0 metadata editors. When you have defined a metadata set, you assign it to an archive which in turn gives users the possibility to view and optionally edit the content of those fields. Users may only edit metadata in an archive if they have been given permission to do so in the archive's access list, but at the lowest level, it's the metadata set that controls whether a field is editable at all.
Creating a metadata set
Assigning the metadata set to the archive
By assigning a metadata set to an archive you control which metadata fields users may edit in that archive (assuming they are allowed to edit metadata in the archive in question, of course) and which taxonomies they will have access to.
What's more, users who are allowed to upload files to the archive will be required to fill in metadata in accordance with the field requirements specified in the metadata set.
Open up the archive properties in the site configuration and go to the Metadata tab. Then pick a metadata set from the drop down list. Click OK to close the archive details page and store the changes.