for example: what is the difference between "Where America is?" and "Where is America?" ?
"Where America is" is not grammatical as a question. In a question with a WH word ("who", "what", "where", "why", "how" etc) we always invert - put the auxiliary (or the verb if it is "be" or sometimes "have") before the subject.*
When we embed the question in a larger sentence, then we don't invert:
Ask him where America is.
[* For yes/no questions, without a WH word, inversion is required in formal language, but optional in colloquial speech: "Did you go?" or (informal) "You went?"]