Use of Cases- The Nominative and Vocative Case

The case of a noun/pronoun/adjective shows its job in the sentence. 

NOMINATIVE

This case is used for the subject of a sentence or clause. It names the person or thing the sentence is about. With an active verb, it refers to the person who does the action: 

puella librum legit.   The girl reads the book.

With a passive verb, the subject is the person or thing on the receiving end of the action: 

liber a puella legitur.   The book is read by the girl. 

The nominative…