Many-to-many relationships between tables are accommodated in databases by means of junction tables. A junction table contains primary key columns of the two tables you want to relate.
Create a third table by right-clicking within the database diagram, and then clicking New Table.
This will become a junction table.
In the table editor’s dialog box, enter a name for the table.
For example, the junction table between the Customer table and the Supplier table is named CustomerSupplier.
You can add other columns to this table, just as you can to any other table.
The creation of a junction table in a database diagram does not insert data from the related tables into the junction table. You can copy rows from one table to another or within a table using an Insert From query.