A nice preview helps you get a feel for what your campaign will look like in inboxes, before you send! When you’re in the composer, click on Preview in the upper right corner of the screen.
You’ll now have the Web View of your campaign open in a new tab, in your browser.
On the bottom of this same page, you can click on the campaign title to reveal a menu of all past campaigns, from your Dashboard.
Click on any campaign title in the list to switch to a preview of that campaign. You can browse through all of your campaign previews on this same page, if you wish.
There's also the option to share any campaign, right from here. Just click on the Share button on the lower right. And to get back to your composer, you can either close this tab, or click the Edit button in the lower left.
Send a test from this page, as well. Just click the Send test button on the left, and enter the test email address.