Let me ease your confusion, Muz123. You'll have to customize the standard or master sales form template.

You can follow the steps provided by AlcaeusF or RoseMarjorieA. It will guide you on how to customize the sales form. The changes will flow automatically in the Purchase Order form.

Once you're ready, you can convert it to a bill. Just open the Purchase Order, then click Copy to Bill.

If you have other questions, please feel free to drop a comment below. Keep safe!