The vocative case is used when you are addressing someone, calling out to him. Nowadays, a lot of people use nominative instead of the vocative which is wrong.

example

  1. Miroslave, stani. (Miroslav, stop.)
  2. Mirjano, dođi ovdje. (Mirjana, come here.)
  3. Nemam novca, Stjepane. (I’ve no money, Stjepan.)