Update: NZBMatrix.com closed down in December 2012. NZBMatrix.eu closed down in June 2013. If the site re-opens again, the information below will likely still be valid:
You can’t download files from NZBMatrix; the site is only an NZB-listing site. In order to use the NZB files that you get from NZBMatrix, you need to have an NZB-downloader program like SuperNZB, and access to a Usenet server.
NZBMatrix lists NZBs which point to the actual files on the Usenet network. So, searching NZBMatrix for a file is very similar to searching Google. The difference though is that you can’t just click through to the file because Usenet isn’t part of the web, and you can’t browse it with a web browser. Usenet came before the web and requires its own special type of browser or “client” software.
Also, files are stored on Usenet in many small chunks. So, the NZB files that you download from NZBMatrix are larger than you might expect. If you open an NZB file with a word processor, you will see all the individual chunks listed. But those are only pointers to the Usenet locations of the real files.
Even if your ISP has a Usenet server that you can use for free, you can download much faster with a premium service like Easynews.