Simple Theme - enabling a Popup Window
From Spiffy Stores Knowledge Base
The Simple Theme allows you to display a popup window that can also contain a subscribe form. It allows you to set a title, subtitle, image, and add a button as well. It's as flexible as we could make it, whilst still displaying beautifully on different devices.
To enable the popup, go to your Theme Editor, scroll down to the "Marketing & SEO" section, tick the "Popup Enabled?" option, and then save your settings.
An easy way to test this feature, set the "Days until popup is displayed again" option to 0... that way the popup will show every time you refresh the page in your storefront.
Popup Settings
Subscribe Form
The subscribe form that uses the settings from the subscribe form in the footer section.