You may want to print invoices for orders via your online store, for your own administration. This can easily be done via the Orders page.
Step 1
From the Editor, go to Store > Orders
Step 2
Click on an order to open it and go to Print > Invoice
These invoices can also be automatically sent to your customers along with the order confirmation they receive via email.
Step 1
Go to Store > Confirmation emails
Step 2
Enable the Attach invoice (pdf) option to ensure customers receive an invoice with their order confirmation