It works the same as the torrent stuff.
You must search for a .nzb file, like you would search for a .torrent file.
Once you have said .nzb file, you load it in the news downloader app.
App will then download it, and perform a few extra steps that is not needed on torrents, eg will put everything together, then extract it, if all went well.
The bigger difference with nzbs are, you have a higher (tho very low) chance of incomplete or corrupt downloads. There is built-in mechanisms to fix this when possible.
So basically, go find a nzb indexing site, download nzb file, add into app, let it download from news server. Done.
That is the simplest way I could explain it.