I really doubt you will find someone here that will give you a step-by-step guide for building a bot. This forum primarily caters to an experienced developer audience. You’re better off using an existing bot, but if you truly want to dive into making your own bot then mIRC is a popular choice. You could ask for assistance on the mIRC forum: http://forums.mirc.com/ubbthreads.php/forums/5/1/Scripts_&_Popups