An invoice is given to a company that purchases items from you. The company does not pay straight away but settles the payment for goods received within a specified time period.

This is how it works:

1. The customer orders items from you
2. You deliver the item
3. You send them an invoice showing the goods you sold and the amount they need to pay
4. The customer settles the invoice by making the payment (usually within 30 days)

The invoice must include your business logo and details and a breakdown of the items and costs involved.

Look here for an example of an invoice.