NewsNation is still one of those services that like to rely on cable/television providers rather than provide their content directly to the end-user via a standalone channel/app (free or subscription).
As such, to answer your question, NewsNation is not free. If you do not have a cable subscription, and you are watching your content entirely via streaming, you will need to subscribe to a "cable-alternative" service that carries NewsNation among its channel line-up.
It seems that you can also watch NewsNation via their website https://www.newsnationnow.com/news-nation-live/, and either cast through your Roku device/RokuTV, or play on a laptop and connect directly to your TV via HDMI cable. (seems to be a continuous live feed.)
I was editing my response as you responded, as it does look like NewsNation has a standalone channel/app available. (looks like abridged content).
It is free to install on your Roku devices. You will not be charged for watching any of the content on it. (I poked around a little in the channel/app, and it looks like it is segments, clips, etc).
I should have checked its current availability on Roku before the prior response, but that was the situation when this question was last asked and the NewNation website still does not mention its standalone Roku channel/app. Not exactly the same as the "Live" NewsNation, but you can watch any of the content in the free NewsNation channel/app free of charge.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102