Which file is responsible for the writing amount for shipping the order form

[mar22]

Hello

First of all, sorry for my english

I plug into orders. I do not know, however, where she writes the amount of shipping which affects the amount to be paid. Maybe it saves in the same place as the VM without a plug?
Can anyone know what file is responsible for the provision of information in the VM?
I suppose that the record is done to cookies in javascript, but how it performs file and through which variables?

I will be very grateful for your help in this area.

Best regards
Marcin