The preview tool can be accessed using the preview button above the main ribbon, and from various other parts of the application. When you use the Preview option, a new window opens to show how your email will look. You can review both the HTML and plain text versions.
If you wish to preview the campaign with some personalized data, you can search for a particular contact by entering their email address, or part of their email address, in the Search for box at the top of the window. Click on the SEARCH CONTACTS button to bring back matching records.
You can click on the SHOW RECENT button to display the ten most recent contacts you imported and preview each one in turn. This is a great way to see how any personalized data fields will look.