It seems that the Urim and Thummim were small objects that the Israelite high priest kept in the flat pouch (or breastpiece) that he wore on the front of his clothing. They were used to find out God’s will in matters requiring a clear-cut decision.
In seeking God’s will through the Urim and Thummim, the priest put a question to God in a form that required an answer of either ‘yes’ or ‘no’. He then took the Urim and Thummim out of the breastpiece to find out the answer. God may have said ‘yes’, ‘no’, or nothing at all (Exodus 28:15-30; Numbers 27:21; 1 Samuel 14:41; 1 Samuel 23:9-12; 1 Samuel 28:6; 1 Samuel 30:7-8; Ezra 2:63; Nehemiah 7:65). (Compare, for example, the drawing of two identical coins out of a pouch. Two ‘heads’ means ‘yes’; two ‘tails’ means ‘no’; a ‘head’ and a ‘tail’ means ‘no answer’.)