MyBB Community Forums

what is difference between category, forum and thread?

why there is no extra table category for categories rather than c/f in forums table?

what is parentlist column in forum table?

Start from the wiki if you do not know the basics of forum: http://wiki.mybb.com/index.php/Main_Page

in addition to the above, the categories and forums are int eh same table so that they can be easily nested.

the parent list defines the nesting of forums in a categroy or other forum.