Weta: Post Slider – Help!

Hello, a simple question I think, but it is frustrating me. How can I add posts to the Weta: Post Slider? I am quite new to WordPress and I am sure I should understand a fundamental to be able to do this but I cannot see how I can add posts to the widget settings? This does not seem to be part of the intro video or documentation – as far as I can see?
Thanks in advance