Add where condition to Form's button

I have a basic Form question -

For lack of not knowing any better, I have created multiple copies of the same form to handle different scenarios.  For example, I have a form name f-order and I have second similar form named f-order_edit.  f-order_edit is opened when a user clicks on a button (located on a third form), which uses a criteria in the f-order_edit underlying query to one return one specific record.

There is probably a better way to handle these two scenarios with a single form + some sort of "where" expression that is associated with the button...right?   Where would this code be placed...on one of the button's events?

Thanks,
Ken