What must to have a discussion to receive many answers?"magic" formula?

The best thing you can do is to just respond to people. Go back and comment if they comment to you, and just try to get exposure that way. Often times people will go back and look at your discussions etc depending on how good your response is. There's not really a magic formula at all. Use the search engine to find discussions that may already be out about something you want to talk about. Respond to it no matter how old, and then go back and find a discussion of interest that each responder to the discussion has made. I hope that I haven't confused you. Long responses are better on making money / understanding.