Tapping instruction please!

[Nima]

Well, some of you know the story; Bolt broke in the head, I drilled out and try to tap it, tap broke in the hole!. I spent all Sun and Sat try to fix it. I bought different type of extractors and etc. Anyways, Now I am at this point; I drilled the tap almost out but the hole is slightly bigger, ofcourse. Now, I would appreciate if somebody explaine to me how to do the tapping correctly. Please explain it in very simple language.
Also, I have another question, is there any product that I can fill the hole with and make smaller hole again! or should I just go with the bi hole.
I appreciate the time. Thanks.