1. Ext Designer is a UI builder for Ext JS that allows rapidly arranging and configuring Ext JS components visually. It generates first-class Ext JS components that can be exported and used in an IDE or browser.
2. The Designer workflow involves creating and configuring components and data stores, exporting to disk, importing into an IDE, and implementing business logic and behavior.
3. Advanced configuration techniques in Designer include function-type component configurations, adding plugins, and integrating user extensions, while still leveraging the visual design capabilities of Designer.