～は 何ですか？（What is ~）

これ

"これ" means "this".

なん

This means "what". This is usually used in a question sentence.

これは　なん　です？

Using "A is B" grammer, I wrote like "this is what." in Japanese. But usually "か" is put at the end of the question, so...

これは　なん　です　か？

Means "What is this?".

おなまえは　なん　です　か？

Means "What is the name?". ”なまえ” means "name". and the first letter "お" is put as extra. Because this is a polite way to say "name" when you ask someone's name.

(wrong)あなたは　なんですか？

This is a wrong example. You can not ask like "What are you?". As in English, "なん(what)" is used when ask about things, not people.