I want to create an excel document that has multiple sheets.
On one sheet will be a database of clients.
On another sheet will be an invoice.

When the user enters the name of the client on the invoice, Excel
should automatically add the address from the database to the invoice.

Does anybody know of any tutorials that explain how to do this. The
tutorial doesn't have to be too detailed, but provide enough
information on how to do it.

I have seen example spreadsheets that do this, but it is difficult to
work out how they have been created.

Thanks