Fernando,
If you're working in a spreadsheet:
Cell A1 contains quantity, Cell B1 contains Unit Price, Cell C1 =A1*B1
Cell C1 will update each time you change quantity in A1.

If you're working in a UserForm:

Item1TextBox.Value = Quantity1TextBox.Value * UnitPrice1TextBox.Value
Item2TextBox.Value = Quantity2TextBox.Value * UnitPrice2TextBox.Value
Etc.
TotalTextBox.Value = Item1TextBox.Value + Item2TextBox.Value + Etc.


HTH
Henry

"Fernando Duran" wrote in message
...
i Don't have much experience in programming, so, i need some help in
technics to do a few things to work as I want to to behave.
Lets say, that in an invoice, every time the user changes data, for
example Qty. the amounts they have to change a the same time.. How can I
get to that point? looks like a loop..

Thanks

Fernando