To access newsgroups, you need special types of programs called newsreaders. Some email programs like outlook etc. too can be used to access newsgroups. However, the best and the easiest way to use newsgroups is from the web itself using Google groups. ‘Google groups’ has a 20 year archive of discussions happening on Usenet and can be a good and convenient place to start using newsgroups.
If you chose to access newsgroups using newsreaders you will need support of your ISP to access newsgroups. Most ISPs provide access to Usenet news server. You have to set up the newreader software to point towards your ISP's newsgroup server and of course have an internet account. If you do not know what the newsgroup sever address is (usually something like news.yourispname.com), just contact your ISP and ask how you can access newsgroups.
Once your software is set to access newsgroups, all you will need to do type in the address of the group, very much like typing in the URL.