well, the session ID should not be used to relate the 2 tables.
you can store the Session in the order table, but it should not be used to create the relationship between the order and details.
the orders.OrderID and orderdetails.detailOrderID columns should be used to create the relationship between the 2.
in the store order summary behavior, set the ID column to the OrderID column of the orders table, this is a primary key column that should auto increment, so you dont need to bind this column to anything in the bindings section. Make note of the session name that will be created to hold the OrderID value in the session section.
in the Store Order Details behavior, the ID column should be set to the detailOrderID column of the orderdetails table. this should be bound to the session created by the Store order Summary behavior.