After the download is complete a list of Subjects will appear. Double-click on a subject that sounds interesting. There's a group named alt.test and another named misc.test. I suggest you post a test message to one of them, wait for your message to show up, and see how it looks before posting to a real group. One final note.
Some people seem to think newsgroups are a place to insult others, sort of a human shooting gallery.
One of the reasons I like alt.home.repair is it has a minimum of these ugly netizens, but they do pop up sometimes. If it were to happen, just remember why you are there, and try to ignore them. Please drop me a note and let me know if you use these instructions and post a message successfully.