How can I test what an email I've created will look like?

The only way to see an email that you have created/configured in the management system is to perform an action on your website (or in the management system) that triggers the email to be sent.

For example, if you've configured an order status email then you should create an order in the management system (that has your email address in it) and then change the order status for the order. This will then trigger the order status email to be sent to you.

Its the same with all emails (so to see the account creation email, you'll need to create an account on your website).