Participation in k12.ed.math takes place in two ways:
(1) Reading the newsgroup
(2) Posting articles to the newsgroup
Some people do only #1. This is known as "lurking".
If you also post articles to the newsgroup, then you will be able to exchange ideas and participate in discussions, ask questions, and so on.
The answers below in this category provide more details on how to participate in the newsgroup.