Post pictures? http://mmb.maverick.to/showthread.php?t=23262 Use the gallery? http://mmb.maverick.to/showthread.php?t=15529 You already seem to have posting messages figured out.
Just pick a forum that is appropriate for the discussion you want to start. For example, if you want to create a technical thread, start it in the technical section.
Go to a forum you want to post in, like the general forum http://mmb.maverick.to/forumdisplay.php?f=2 Then click on the new thread button