Inputting Multiple entries using a form.

[Andy]

I a bit of a novice at access, so sorry in advance for
making your read this, but I'm really really at a loss for
how to do this.

I want to input details of charges into a database using
the same invoice number where I have 3 or more charges
(each with different VAT) on one bill.
I have tried using a subform to do this but it is not
working for me.
I have a main form for entering a single entry so that
when the info is entered it filters into another form
which I print off and give the another user in a format
they want.
With a multiple charge I need to enter the invoice no and
the customer but when I get to the charges I want to be
able to input each charge individually. When finished
inputting i want the form to ask if there are more charges
for that one invoice no to be input & if so give another
input screen,If not I want to be able to return to the
main forn and see the total for the bill gotten from the
inputting.
I struggled my way through the single form but I'm lost as
to how to go this.
If anyone can help, please do so.
Thanks
Andy