There are two standard emails built in to WooCommerce that are sent to a customer on a successful transaction.
The first is the Processing Order email. It is and sent automatically as soon as a payment goes through.
The second is the Completed Order email, and is sent manually by the site owner when he/she marks the transaction as complete in the back end, (which generally means when the goods are dispatched).
If you are happy with the standard text in those emails, then all is well.
If you want to change the text to suit your style or how your shop operates, then unfortunately, there is nothing in the WooCommerce admin page where you can change the body text of those emails.
If you google for how to do it, you will see reference to changing core templates and translation strings, all of which are more complicated than using the Email Text Customizer plugin.
With the plugin activated, there will be a new field where you can change the body text of the emails.