SQL & PL/SQL

Hi
I am working on the interface very first time.
what i understand is as follows:
Data file--> Control file --> staging table --> pre-interface table-->interface table then run import program.
Interface tables:
AP_INVOICES_INTERFACE
AP_INVOICE_LINES_INTERFACE
Base Tables
AP_INVOICES_ALL
AP_PAYMENT_SCHEDULES_ALL
AP_INVOICE_DISTRIBUTIONS_ALL
API / Import program: Payables (Invoices ) Open interface
I would like to create the invoices for vendors from different cities. So from data file how many control file I should create? and how many staging tables I should create? Can anybody please explain me how to proceed right from Data file--> Control file --> staging table --> pre-interface table-->interface table ???