How i can place online users & forum stats on the bottom of all pages of my forum?(like on here this forum) i tried plugin from marketplace but it said i dont have permission.

While I'm not posting in relation to your question, the various plugins available in the Marketplace only display users online/browsing. If you add the plugin to a particular forum, it will display "global" users, not users browsing that particular forum.

I share the same concern as fahim pk