Once you have installed and activated WordPress Popups you can navigate to Popups -> Settings to enter your license key. The license key could be obtained in your account page.
Also if you wish to track popups impressions and conversions with you Google Analytics account you will need to enter your UA-XXXXX property code in the UA code field.
You can also disable the automatic styling of the social icons if you use them and you can unload the javscript for the social icons in your are using your own.
By default you will just need to enter your license key on this page and you will be ready to move the the quick usage guide.