A pop-up widget is a widget that your visitor will see when they first arrive to your site. A pop-up can be a great tool, because it can't be ignored. This page can be used as a call-to-action like gathering email addresses from visitors, highlighting a track from Soundcloud, or asking for a Facebook like.
Here are some examples:
Setting up a pop-up works exactly the way as setting up a widget.
Click on Choose widget:
And select the widget of your choice. Enter the required information and you are set.