Once the extension is installed successfully, go to Stores>Configuration to configure the extension for use.
Enable: Enable or Disable the extension from here. Set it as enabled to use the features of the Magento 2 Newsletter Popup.
Popup Delay: Admin will have to add the time they desire to display the popup on their frontend of the store.
Popup Title: Add appropriate title according to your requirement here.
Popup Text: Add appropriate text according to your requirement here.