Foreign Key Relations

I am creating a table that holds customer dlv mode combinations, calling (named CustDlvMode). I want to have foreign key relations to AccountNum on CustTable and Code on DlvMode - these are the primary key fields of these tables.

When creating the relations I have the options Normal, Field Fixed, Related Field Fixed and Foreign Key.

By using Normal I still seem to get the constraints I need on the data I can insert into my new table.

My question is what Foreign Key does that Normal does not? Are there other constraints that I do not get by using Normal?