Built-in Newsgroup Client
If you are using Windows Live Mail or Lotus Notes, they have built-in newsgroup clients so you do not have to download the client from the internet separately to install and start discussion. You should first check of your system has a built-in a newsgroup client. Otherwise, you will need download a client and install it on your system to enable you to contact to these groups.
Open Source Clients
You also have an option to download open source clients, which are developed by third parties and are regularly developed by people around the world. Some of them are Mozilla Thunderbird, KNode, Arena and Pan. Although they do not have the same level of quality as does the Windows Live Mail or Lotus Notes, still you can download them for free and install on your system. Since being open source clients, they also vary in functions.
If you do not want to download the client and install on your system, you can use web-based newsgroups clients. Some of them are free to access and use, and have the same level of quality as does a downloaded client. They are simple interface, where you can chat with people from your area of interest online for free.
Almost all these clients are free to access, and you can try each one of them and once satisfied with quality of one of them, select it for regular use. However, there efficiency can vary at time to be of a better quality and on other lower down in the service quality. Generally, people use Windows Live Mail, since they are not open source or open end clients and there are no issues such as frequency updates download, and the quality of service is also tested and proven.