A commercial invoice is typically used for exporting goods internationally. This commercial invoice template includes spaces for the names of the individuals or businesses involved in the transaction, the items being shipped, where the items were manufactured, and Harmonized System (HS) codes for the items. This is essentially a customs declaration stating the value of the goods being shipped.
You may still be mailing paper invoices or you may be doing all your billing and payments over the internet, either using a website that accepts charge cards or an online payment system that uses email like PayPal. As a freelancer, this affects the part of your invoice that lists how you want to get paid. You may even offer your client a variety of payment options, and all of those should be mentioned on your invoice.