Yoma, Chapter Seven, Mishnah Five
This mishnah completes the first seven chapters of Yoma, all of which dealt with the Temple Yom Kippur ritual.
1) The high priest performs the service in eight pieces of clothing, and the common priest in four: in tunic, breeches, a headdress, and a sash.
2) The high priest adds the breastpiece, the ephod, the robe and the frontlet.
3) In these were the Urim and Tummim inquired of. But they were not inquired of except by the king, by the head of the court or by one whom the community needs.
Sections one and two: The first two sections of the mishnah outline the difference between the clothes that the high priest wore on normal occasions throughout the year (not on Yom Kippur), and the clothes that a normal priest wore. The high priest has eight pieces of clothing (see above 3:4) whereas the normal priest has only four pieces. These are all discussed in Exodus 28
Section three: The Urim and Tummim, the oracular stones used in the First Temple, are only asked questions when the high priest is wearing his eight pieces of clothing. And not anyone can ask a question of the Urim and Tummim. Only the king, the head of the court or other high officials of the community may ask questions. For more information about the Urim and Tummim, how they are understood by modern biblical scholars and how they are understood in the aggadah, I suggest consulting the Encyclopedia Judaica.