Can you clarify if you're trying to get help with how to use mIRC or use Mibbit? I've not used Mibbit, so I don't know if they have a place explaining how to use it.
At the top of this website the link "Help" (not the lower help that explains how to use the forum) has quite a few links that include basic and more advanced topics. Including
https://www.mirc.com/ircintro.html
and
https://www.mirc.com/install.html
That top link is even intalled as a .chm file in the MIRC folder