Could anyone tell the definitions of 'tone', 'register' and 'style' and the importance of them in writing a good essay? Any difference between 'tone' and 'style'?
The "tone" of a piece of writing is whether it is angry, funny, ironic, sarcastic, and so on.
The "style" is the way in which it is written - the way in which the writer uses words, grammar and syntax.
I am not sure that "register" can apply to written material. It usually refers to spoken language.