Cheers. Hmmm how to explain...
The newsgroup servers (such as Astraweb / Giganews / Supernews etc) are the servers that actually host the content. Newsbins & NZBmatrix are indexing? sites that point you to the files you want to download... something like that.
From a torrent comparison... Astraweb is the other users your downloading off (but its a server this time), NZBmatrix is the torrent website like piratebay/btjunkie
I'm sure someone will have an better explaination