You can delete both read and unread messages. You may check your newsgroups daily or occasionally, setting your newsreader to purge older messages. Newsgroups are divided into category types, then subjects, and even subcategories. The category type comp is for anything relating to computers, biz is for business topics, news is for discussion of all things relating to Usenet newsgroups, from their administration to policies on how to create new newsgroups. In some categories, creating a new newsgroup requires an approval process that includes voting by interested individuals.
Any message sent is referred to as an article.
And if you get tired of it all, you can unsubscribe and move on to other topics of interest. Again, similar to e-mail lists. But the big difference is that anyone can subscribe to a newsgroup and read the messages. E-mail lists can be limited to a certain population. You can't subscribe to it - you have to be added by the list owners.