On the "front page" of the Microsoft Communities
(http://www.microsoft.com/communities/default.mspx) there's a link on the
left side to "User Guide" with entries for "Getting Started" and
"Newsgroups". These pages should answer your questions about how newsgroups
work.
A searchable archive of the newsgroups is at http://groups.google.com, and
you can follow the link to "Groups Help" next to the Search button for
instructions.