Recommended article before setting up: Engage: Page Targeting

The Newsletter modal is a polished and convincing way to make your users aware of your available newsletter, with easy ways for them to subscribe using their email address or social media logins. To use this CTA, select the Newsletter Modal option.

To use this call to action:
Set the appropriate text, font size, and colors
Choose an appearance, condition and position (see: Editing Your CTAs)
Choose a Lead Form (see: Understanding your Lead Forms )
See Also:
Introducing the Engage plugin
Editing your notification sending options
Connecting A Lead Form notification to your Lead Form