There sure are a lot of newsgroups, but when you open the newsreader it only shows the groups you are currently subscribed to. When your account was created, it was automatically subscribed to a few groups. To see a list of all available groups, press "y" to "yank in" all the groups. Scroll through the list and press "s" for ones you are interested in. Then when you next read the news, you'll see only those subscribed groups. You can unsubscribe by pressing "u".
Note that subscribing to a group places the newsgroup on a "short list", so you can access it more easily. In addition, your newsreader will keep track of messages that you have already read so you wont have to deal with them again (unless you wish).