To start Blogging go your own Spark Page and there should be a "create new blog" button on the right. If it's not there on the Spark Page you might need to select something like "Show more blogs" first.
You seem to have figured out message boards, this is one here! :) You can hit the "Reply" button to make a response to someone in the same 'thread' (message page), or you can hit "Create new topic" to start an entirely new thread yourself if you have a new idea to talk about.
Deb, in New Zealand