What Is A Speed Controller in A RC???

Welcome to RC India

I have changed the topic name from "Hello" to a more "to the point" topic name.

And to answer your question...  http://www.rcindia.org/beginners-zone/doubt-about-esc's/

You can get a lot of information just by searching... like this http://www.rcindia.org/search2?search=electronic+speed+controller

To anwar, thanks for your reply, its really useful