The USCCB has a FAQ at
usccb.org/issues-and-action/marriage-and-family/2014-2015-synods-of-bishops-on-the-family.cfm
It includes this:
What is the purpose of the III Extraordinary General Assembly of the Synod of Bishops?
The Preparatory Document described the purpose of the III Extraordinary General Assembly as “to define the ‘status quaestionis’ [current situation] and to collect the bishops’ experiences and proposals in proclaiming and living the Gospel of the Family in a credible manner.” The Instrumentum Laboris said that the III Extraordinary General Assembly “will thoroughly examine and analyze the information, testimonies and recommendations received from the particular Churches in order to respond to the new challenges of the family.”
**What is the purpose of the XIV Ordinary General Assembly of the Synod of Bishops?
**The XIV Ordinary General Assembly of the Synod of Bishops will continue the work of the III Extraordinary General Assembly by “reflect[ing] further on the points discussed so as to formulate appropriate pastoral guidelines” for the pastoral care of the person and the family (Instrumentum Laboris, III Extraordinary General Assembly of the Synod of Bishops).
What is the relationship between the III Extraordinary General Assembly of the Synod of Bishops and the XIV Ordinary General Assembly of the Synod of Bishops?
The Instrumentum Laboris for the III Extraordinary General Assembly notes that the work of the Synod of Bishops “is to take place in two stages, forming a single organic unity.” The Extraordinary General Assembly could be understood in a certain sense as a preparatory step for the Ordinary General Assembly. At the Extraordinary General Assembly, the bishops will define the current state of the family and challenges that face it; at the Ordinary General Assembly, the bishops will formulate pastoral guidelines to respond to those challenges.