Turbine's official The Lord of the Rings Online: Shadows of Angmar website has been updated with an overview of combined-effort attacks, which the game calls Fellowship Maneuvers.
Teamwork in combat is the basis of the Fellowship Maneuver system; the more coordinated your fellowship is, the more powerful the results can be! Fellowship Maneuvers can also be used to make up for gaps in a fellowship's abilities. For example, healing-based Fellowship Maneuvers can be life-savers for a fellowship that doesn't contain a dedicated healer.
When you trigger a Fellowship Maneuver, a Fellowship Skill wheel appears on each fellowship member's screen asking them to choose how to contribute to the Fellowship Maneuver.