French language Q&A Forum

What is the difference between C'est quoi ? and Qu'est-ce que c'est ? and in what context we use them? Both of them seem same to me in English. 

Thanks for helping

I have a student who was taking an A0 test. She was asked how to say "Marie, you are a student." and was given the prompt 'Marie tu...'. She answered 'Marie tu es élève.' and Kwizbot told her that she was wrong, that it should be 'Marie tu es étudiante." Why would 'élève be incorrect? I was under the impression that they were interchangeable, so I need to understand the usage differences...

Isn't the tu-form of aller "vas"?