JOEL - I assume you are talking about the Seventy quorums? The First Quorum of Seventy constitutes a third presiding quorum over the Church after the First Presidency and the Quorum of the Twelve Apostles (D&C 107:24). A presidency of seven, all seventies and members of the First Quorum, preside over the other quorums of Seventy.
Seventies of the First quorum serve until they are 70 years old and then are put on emerites status.
Members of the second quorum serve for 5 year terms and are usually called to preside over mission areas of the church throughout the world. Members of these two quorums are considered General Authorities of the Church.
During the past few years six more quorums of Seventy have been organized, containing about 200 men who are ordained "Area Seventies". These men live and serve for a certain number of years in their home areas rather than traveling throughout the world.
A good article about the Seventy that will answer your question is in the following Ensign article:
Earl C. Tingey, "The Quorums of the Seventy," Ensign, Aug. 2005, 48