You can attach files—such as a detailed time report, design drafts, or additional project information—to an invoice before sending it to your client. You can also attach an Expense Report, which will contain receipt images entered with your expenses.
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.