This should help get you started:
http://www.mvps.org/access/netiquette.htm
The mvps site has many other helpful links for Access, the Microsoft
relational database program (actually, it is a RDBMS, or Relational
DataBase Management System, which is the term used in the link above).
You should select a newsgroup of interest, and browse the threads to get
an idea of the questions asked. Before posting a question you would do
well to check Google groups to see if the topic has been addressed (many
have been). In general you will get the most helpful responses if you do
what you can do answer your own questions first.
I think plain text messages are best for a newsgroup. I think HTML will
work, but it doesn't gain you anything that I can see. In any case you
cannot add attachments to messages in the Microsoft groups (or other
groups, I expect, but I am not sure about the details).
The main thing when asking a question is to be specific, and to provide
enough details. The link above discusses this point in some detail.