Yes, select a template and then click on the image on the right side of the screen. That will display a full preview. You can also toggle between the "Email" and "Direct Mail" buttons above the picture to see the different forms of communication.
You can also send yourself a test email or text in the "Confirm" step of the campaign. Underneath the message preview, you can click "Send Test Email" or "Send Test Text Message." Just type in the email or cell number you'd like the message to go to.