how can make excel put a serial nomber for the voucvhers?

Answer 1

Your question doesn't really provide enough detail, but assuming each voucher is on a separate row of a worksheet, then if, say cell A1 contains the first voucher's serial number, and each successive vouchers serial number equals the previous serial number incremented by 1, then put the following formula in A2 and copy and paste down as many rows as you want:

=A1+1

Answer 2

You have to use vba for that. The other way is to create a sheet with the latest serial number appended in a new row. You now have a long unbroken list. It cames useful to track the vouchers you made later.
On the voucher sheet, create a max() function. This will put the highest serial number which so happens to be the latest new number.
Print out the voucher, copy the voucher details, paste it back to the summary sheet. Use paste transpose to get it right. You can use fancy lookups to automate further.

Example is attached.

URL is updated.