The following instructions are for: Responsive 6.0+, Mobilia 5.0+, Retina 4.0+, Parallax 3.0+, Turbo 2.0+, and Artisan 1.0+. If you're on an older/pre-sectioned version, please update your theme.
You can add custom content to the newsletter popup to encourage your shop's visitors to subscribe to your newsletter.
From your Shopify Admin, choose Online store > Themes > Customize.
Click Theme settings > Popup/Newsletter.
You can check off 'Enable Popup' and configure your popup here. You have the ability to add in heading, text, an image, and the newsletter form.