how to do Billing using data grid view C# Winform?

Hi friends

I need to creating form which should perform the billing. i need to do billing by using data grid view. how to do it.

For example.

I have four columns in data grid view. that are Item,  Quantity, unit rate and amount.

so the "Item" column will be drop-down. it should be bind with item table. when i select item from drop-down other values will be picked from item table and amount will be calculated automatically. then the focus will be in next row of data grid view.

please any one give me some idea how to do it.

Thanks in advance.

faisal