Having added a field to a metadata editor in the Metadata editor designer, you can click on that field and click on the Item properties tab in the side panel. There are several options there that relate to how QuickLists behave for that field:

Item has a QuickList: When this option is enabled users will be able to predefine QuickLists and thesauruses for this field. The QuickList controls appear next to the field in the editor.

Allow to edit QuickList: To allow users to add content to QuickLists, make sure this option is enabled. If the available predefined metadata should be fixed, an administrator can ship a FotoStation configuration with QuickLists but not allow users to add new content to that QuickList. In that case, you can disable this option.

Auto add to QuickList: When this option is enabled, any content that a user adds to the field is automatically added to the QuickList for quick tagging the next time the same tag is used.

Sort QuickList: When this option is enabled, the entries in the QuickList are sorted alphabetically.

Tip: To enable QuickLists for several fields in an editor layout, select multiple fields using Ctrl / Command and then enable the QuickList options under Item properties as described above.