The Aes Sedai believe that the Ter'angreal allows someone to come face-to-face with their greatest fears (and desires), and the books never really explain the Ter'angreal properly because no one really knows. But based on what the show gave us, I have a theory that the Ter'angreal (at least in the Show) are very much like Glass Columns and are in a way related.
The purpose of the Ter'angreal can be divided into two phases:
(1) You face your greatest fears and desires, and then run away from them (the Testing), because the Ter'angreal gives you a way out.
If you don't do (1), then the Ter'angreal will then proceed to
(2) Make you face and understand the consequences of your greatest