When you are creating an order in POS and you are at the last step, where the customer needs to pay, you have 5 different options:
If you click on Receipt you can print the receipt for the order, when finished click on Done.
If you click on the box right next to E-mail receipt you can add a E-mail that you want to send the Email Receipt to, after that you click Done.
If you wish to print an Return label or a Invoice (A4) you can also do that, by clicking on one of them or both, if you need both. When you are done you click on Done.