DejaNews has a special feature to help do that. The first part of each name describes the content. Soc identifies groups dealing with social issues. News flags groups concerned with the network itself. Talk groups debate issues.
Rec groups deal with the arts, hobbies and recreation.
Some identify the country. Clicking the name on your computer screen takes you quickly to the specified newsgroup. There you can easily follow the thread of the discussion underway, from message to replies. You may also post new public messages, or reply publicly or privately to the person whose message interests you. To save time, on subsequent visits you can elect to see only mail posted since your last visit.