Pageviews count +1 every time a page is loaded on your website.
Displays count +1 every time a pop-up is displayed.
Clicks count +1 every time one of your visitor click on a call to action (sign up, image, etc.). This excludes clicks to close the pop-up.
Emails count +1 for each time you collect a new email.
CTR is the Click Trough Rate, i.e. Clicks/Displays.