I worked out a tutorial with screen shots on how to implement a many-to-many relationship in FileMaker Pro 11.  It is available here as a .PDF .  A classic example of this would be a situation where you have a board of directors, which also has committees.  Typically, a board member might serve on more than one committee, and of course a committee has more than one member. In a relational database this is defined with three tables,  one for the board members,  one for the committees,  and an intersection or “join” table, that holds information from the two other tables.

Excruciating details here.