First,go to sales.
After that click orders.
To manage invoice for customer, click this button.
Go to add order history.
You can choose either to notify customer about the status order or not.
Write your courier service and airway bill in the comment.
After finish complete form for order history, click blue button at the right side to add to history.
Click this green button to generate invoice.
To print invoice for customer click this blue button.
This is the invoice. To print it press ctrl + p.