Uptdate Two Tables With Button On Form

tables being updated are products_ordered with productID, orderID and Quantity and orders with orderID, customerID and todays date in to products_ordered.date


form
name Value
orderID =Max([orderID])+1
customerID SELECT Customers.customerID
customer_name Customers.customer_name
inv_address Customers.inv_address
Inv_city Customers.inv_city
inv_region Customers.inv_region
postcode Customers.inv_postcode
orderID

Order Details Extended subform
productID SELECT Products.productID
desc Products.desc
finish Products.finish
price Products.price
quantity quantity

there may be more than one productID and quantity as more than one product can be on a single orderID

Oh and I use a combobox to chose customer ID which fills up the other firlds in the form and another combobox in the subform to chose a product which fills up the description field. they start up with fields already filled with data how do i start the form blank?