Before sending out an email it´s always comforting to be able to see how it will look in the recipient's inbox.The preview feature has two different paths, the first one is sending the actual email to yourself or a collegue. The second one is to preview the email in the browser.
Sending a preview email or previewing in broswer
When inside the email editor find the button called Preview in the top section, click it.
In the dialog that appears there's two options, either enter the email adresses that should receive your preview emails, or click the button in the bottom called Preview in browser:
Preview email in browser
Follow the steps above, but click the Preview in broswer button. In the preview window that appears you can drag the corners to expand or minimize the screen size. The templet will render accordingly and you will be able to see how it will look on a smaller phone screen compared to a larger computer screen.