The Billing component will look and behave differently depending on whether you are an Internal user or a client. Most importantly, internal users have the ability to send invoices and subscription invoices. They will also see all of your company's invoices. Whereas, clients will only have the ability to view and pay their invoices.
Internal users can see invoices created in your Stripe account in the Billing module.
If an invoice is in the Draft state, you can move it to the Open state by clicking the Actionmenu on the invoice and clicking Send. This finalizes the invoice which means it can no longer be edited.
If you are using Stripe your invoice will be sent via email within an hour. However, it will be visible in your customer's portal immediately, in the Open state.
When a client pays an invoice it will move into the Paid state.
Depending on your rules with your payment provider you can automatically move your invoice to Void if payment is not made after a certain time. You can also manually void an invoice.
Subscriptions (Stripe only)
If you have connected your Stripe account you can also view recurring invoices (or subscriptions).
Subscriptions behave almost identically to invoices except you can additionally see whether it recurs weekly, monthly or annually/yearly.
Invoices are automatically branded according to your Stripe/Quickbooks settings. For more details visit their corresponding support articles (Stripe / QuickBooks)