I got the answer directly from them:
1.4 Can I use the Usenet.nl software with Linux?
But as our product only provides the access to the usenet, you may use every other newsreader. Change the servername in the set up of your newsreader to news1.usenet.nl, use port 119 or 443 and enter the access information for the Usenet.nl-client (email@example.com).
About the meaning of those words, I don't even know what a newsreader is!