Master Table with 2 detail tables

I have Delphi2, Win95, and InfoPower 2.0

My application has one table (Sales) that has two detail records.

Sales ----Line Items
Sales --- Payments (used in the case of layaways, where there is multiple
payments).

I have everything tied together as far as the master/detail(s)  relationships
go...
My question is how to I do database processing.  I have one DBNavigator
control, and that is all that I want.

For example, on a save on the master record, what commands would be issued
on the detail records?

Do I tie them in to Post processing events on the Master Table?

Please be explicit...

Thanks
GMAN