Help me, give me some idea who to make a site like www.debate.com, where people can vote in favour or against, people can register and have thier own debates private or public.

You are asking an over generalized question. I suggest you learn PHP.

A few things you may want to look into, and ask on a per-question basis:

How do I make a PHP poll?

How do I create a message board?

and

How do I create a log-in script? (if this is not already included with the message board script)