Once you've begun reading an article, you have another set of commands available. Most of these are paging commands, allowing you to go back and forth within an article, much like using the Unix utilities 'more' or 'less'. Other commands skip to the end of the article, then behave as if you'd typed them at the article-selection level. Probably the most useful commands in this level are those which you can also type at article selection level, such as search commands. You can mark all the articles in a newsgroup unread, if you like.
Most people just look for a single article, though.