Answer:
Today the members of the First Presidency and Quorum of the Twelve Apostles hold these same keys (see Doctrine and Covenants 90:3–4, 6; 107:35; 132:7). These keys are the authority God has given to priesthood leaders to direct the use of His priesthood on earth.
The Mississippians were a native American culture that inhabited the Mississipi River Valley and surrounding areas from 9th till 16th century. Their culture was unique in that they created Mounds, that is man-made hills, many of them are still existing today.