First you have to make sure you installed 2 required plugins “Elementor” and “PopBox For Elementor”. If you haven’t you can do that via Appearance > Install Plugins.
Next you have to create a page using Elementor.
To create a popup, look at widget panel on the left and search for “popbox”
Then drag widget to page content area on right side. It will open widget’s settings.
Now you can start design popup columns & layouts using all Elementor widgets and customise its settings.