The true Church of Jesus Christ must have Prophets and Apostles. Christ set up the Church this way when He was on the Earth, and He is the same yesterday, today, and forever. (Hebrews 13:8,Mormon 9:9)
Once upon a time the Children of Israel were met on the battle field by Amalek. During the battle we see how the First Presidency of the Church works in unison.
"And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed.
So we see that Moses was the Prophet at the time, and he had two others by his side to help him.
President Henry B. Eyring, President Thomas S. Monson, and President Dieter F. Uchtdorf. President Monson is the Lord's Chosen Prophet on the Earth today.
The First Presidency presides over the entire Church, and is directly over the Quorum of the Twelve Apostles.
The members of the Quorum of the Twelve Apostles are, President Boyd K. Packer, Elder L. Tom Perry, Elder Russell M. Nelson, Elder Dallin H. Oaks, Elder M Russell Ballard, Elder Richard G. Scott, Elder Robert D. Hales, Elder Jeffery R. Holland, Elder David A. Bednar, Elder Quentin L. Cook, Elder D. Todd Christofferson, and Elder Neil L. Anderson.
There are also Seventies, who are assigned to manage things in specific areas around the world, and to help the Quorum of the Twelve Apostles. The Presidency of the Seventy is over all other Seventies. There are Seven Presidents, and no counselors, in the Presidency of the Seventy.
The Presiding Bishopric is the presidency of the Aaronic Priesthood throughout the Church. The Presiding Bishop and his two counselors also serve under the direction of the First Presidency to administer the temporal affairs of the Church.
You can view a picture of each of the General Authorities at: http://lds.org/church/leaders?lang=eng