Question
Could you please tell me how the Urim and Tumin (the High Priest’s breastplate) worked?
Answer
The Urim and Thummim were 12 precious (or semi precious) stones which were attached to a breastplate worn by the Kohein Gadol (High Priest). Each stone had the name of one of the Jewish tribes engraved upon it. For the most serious questions facing the Jewish Nation there was a process by which questions could be directed using the Urim and Thummim, and answers would come back from G-d by some of the stones lighting up in a particular order.
Regards, Eliahu Levenson