Once you finish the final touches of your Email in ContactMonkey, click Preview at the top right of the page. This will show you how your email will look on mobile and desktop. There is also the option to preview the email in dark mode, which you can read more about here. See below desktop view:
And mobile view:
If you are happy with how the email looks. Click Save and Exit at the top right of your screen. This will save your latest change and bring you out of the email so you can send it. 
For information on sending your email, check out this section of our help centre.