They're designed to bring a new user up to speed without having to repeat the same answers every time a user asks. Every group has a topic. When posting, please make sure your posts falls within the topic of the group. If it doesn't, look for a different group that is closer to your topic. If you want to point out that you're new, simply wait until you post on a real topic and just mention it.
Many sites pay for their feed and the greater the volume, the higher the cost.
So, please, try not to post wastefully. It's the Usenet equivalent to shouting, and is considered very impolite. In general, just try to be considerate of the other members of the nets. There are many programs that allow you to access the Usenet newsgroups, generally referred to as news readers. The first time you do so you will see a greeting screen, be sure to read it.