Details about the archive appear in question 5.1.2. Question 5.2 has a list of other network resources, e.g. newsgroups, with related material.
If you're not sure where to look for an answer to your question then check out the lists of related network resources in section 5. There is information there about what newsgroups to read, to post to, as well as what essays and lists are available electronically to help answer your health and body related questions. Question 5.2.4 is the most general.
If you do ask a question by posting please remember to request that replies be sent to you by mail so that you can summarize them for the rest of us. Be sure to say something like `please reply by mail, I'll post as summary,' or it is likely that someone will think that you want replies by mail only because you are too lazy to read the group -- I kid you not. When it comes time to post your summary take some time to actually summarize the mail you received. It isn't necessary to specify who gave each answer or to quote them exactly. Do not concatenate all the messages into one posting! By taking the time to make a proper summary you are helping all the present and future readers of alt.backrubs. That group includes the people who took time to write to you. Much more advice about how to best work with the Usenet community can be found in question 1.4. The archive is the subject of question 5.1.2 (in section 5).
Whoever is providing you with access to Usenet should be able to give you some basic introduction or instruction. This isn't because they are necessarily nice, but because if they don't at least attempt to tell you the basics then they can't blame you when you do something awful. If they haven't offered you any advice or instruction then ask someone responsible for some pointers to useful information. I advise you not to ask another newcomer -- that is a great way to propagate misconceptions.
There are many introductory books about the global Internet and Usenet. If you learn well from books then you might consider buying one or borrowing it from a library. Some books are available for free, others are available for sampling online as an enticement to get you to buy them. For a fuller discussion of such books see a) the misc.books.technical newsgroup, b) the Unofficial Internet Book List at the rtfm.mit.edu FTP site (filename book-list in the directory pub/usenet/news.answers/internet-services). See question 5.2.4 for more information about the rtfm.mit.edu FTP site.
I don't like to duplicate information that is available in more general frequent postings. Instead, I direct you to the following three documents. This list was current as of 9 October 1995.
news.admin.net-abuse FAQ (1/2) and news.admin.net-abuse FAQ (2/2)
The latest copy I have was posted to news.admin.net-abuse.misc, alt.current-events.net-abuse, alt.answers and news.answers by Scott Southwick <scotty@ancho.ucs.indiana.edu> at 23 Aug 1995 22:36:17 GMT and 23 Aug 1995 22:37:18 GMT (with Message-IDs <41gah1$m19@usenet.ucs.indiana.edu> and <41gaiu$m6s@usenet.ucs.indiana.edu>), respectively.