The primary key is the field or combination of fields that uniquely identifies each record. For example, you might use both an employee number and name, because a database could have two employees with the same name. You might already have defined a primary key in your database table.
What to enter as default values for the primary keys (on the next screen)
After you define the primary key, the wizard prompts you to choose default values for each field in the key.
When you enter values for each primary key, you associate the shapes with specific records in the database.
When you choose None and don't enter values for each primary key, you associate the shape with fields in the database table, not specific records or data.