The nominative case is used for the subject of a sentence β the person or thing performing the action.
If you know a word is the subject of a sentence, then it takes nominative case.
To identify the subject, ask 'Who?' or 'What?'
In Bosnian: Ko? (Who?) or Ε ta? (What?)
π‘ Think of the nominative as the "dictionary form" of words β it's how you'll find them in a dictionary!