Create a related table.
You will have:
a Member table, with a MemberID primary key.
a Position table, with a PositonID primary key.
a table of MemberPosition table.
The 3rd table will have fields:
MemberID who this entry relates to
PositionID what position this member holds.
StartDate when this member commenced in this position.
For the interface, you will have a main form bound to the Member table, with
a subform bound to the 3rd table. The subform will be in continuous view, so
you can add as many positions as apply. In the subform, you will have a
combo box that uses the Position table as its RowSource, so you can select a
position from the combo, on as many rows as you need.
Tehnically, the 3rd table is called a junction table, and this is the
standard way of resolving a many-to-many relation into a pair of one-to-many
relations. For another example, see:
Relationships between Tables (School Grades example)
at:
http://allenbrowne.com/casu-06.html