The way one "starts" is to do exactly what you are doing, that is, posting to the forum. People post when they feel moved to do so, perhaps when the subject is interesting, or when it is irritating, or is a subject they know well. There is no requirement or compulsion to post, and many read a lot, but post little. If you have a specific question, post it in the appropriate forum. Otherwise, read any posts you find interesting and post a reply as you see fit. :0)