For any type of business to succeed, you have to get paid. So whether you do one freelance gig a month or run a full-time writing business, you need to calculate the time you've worked and bill your clients for it. That means you need to know how to write an invoice.
If you're a company that plans to extend credit to your customers, you'll have to get familiar with invoice generation. The invoice is a bill to another business that lists the total amount due along with a breakdown of the items purchased. When it's time to generate invoices to send to your customers, you can make the process simpler by using templates in Microsoft Excel.