for this you need to use a linking table in order to create a many to many relationship:
memberID - Primary Key
categoryID - Primary Key
memberCategoryID- primary Key
memberCategoryMemeberID - relates to members.memberID
memberCategoryCategoryID - relates to categories.categoryID
you would need to use the manage relational table behavior in data assist to manage the linking table.
Andrew reed posted a good guide for the manage relational table behavior in this thread: