The confirmation emails are sent automatically to your customers after an order is made. If the order appears in your Orders section, then the email was definitely sent to them, it must have hit their spam or an email filter like BoxBe. You can resend the email confirmation by clicking the Resend Confirmation icon to the left of each order in your Orders section, or you can forward your order confirmation to them manually.

If the order does not appear in your orders section but you have received payment, then the problem is to do with you PayPal not sending us a notification of competed payment. Read this FAQ, this could stop the problem from happening in future;