The usenet info centre at
http://sunsite.unc.edu/usenet-i/usenet-help.html has a number of
introductory documents.

You should also subscribe to news.announce.newusers , and look for these
documents:
   * A_Primer_on_How_to_Work_With_the_Usenet_Community
   * Answers_to_Frequently_Asked_Questions_about_Usenet
   * Emily_Postnews_Answers_Your_Questions_on_Netiquette
   * Hints_on_writing_style_for_Usenet
   * Introduction_to_the_*.answers_newsgroups
   * Rules_for_posting_to_Usenet
   * What_is_Usenet?
   * DRAFT_FAQ:_Advertising_on_Usenet:_How_To_Do_It,_How_Not_To_Do_It

If you only have email access send mail to mail-server@rtfm.mit.edu with
the following lines in the message:
    help
    send
usenet/news.announce.newusers/Introduction_to_the_*.answers_newsgroups

If you have any questions a good place to ask them is the newsgroup
news.newusers.questions