the Urim and Thummim: These are Hebrew terms that might translate as lights [or curses] and perfections. These objects were likely two stones. The priest used them to receive a yes-or-no answer from God.
The Bible does not describe what these stones looked like. Other passages further explain their use (see Numbers 27:21; Deuteronomy 33:8; 1 Samuel 28:6; Ezra 2:63; and Nehemiah 7:65).