I search in google classifields plugin for mybb forum but never find anything. If it have this plugin somebody can send me link?
IIRC, classified plugin does not exist for MyBB. however there are a good number of plugins to show couple of advertisements.
You can configure MyShowcase to be a simple classifieds. No section support but titles, descriptions, comments, images,searching, etc are all built in.
Find it in the market on site in my Sig