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.
While you can make up your own invoice or use a free template, it's often easier to use an invoicing system that offers more in depth features. Some invoice systems, like Harvest, offer the option to create estimates for big projects, keep track of multiple clients and send reminder emails when payments are late. Another option is Freshbooks, which offers similar features but includes profit and loss sheets, as well as trackers to help you manage your time. Both of these services can be used for free or upgraded for a small fee, and include lots of other cool features, like scanning receipts for work completed in the field.