The nominative case is used for the subject of a sentence—the person or thing performing the action.
If you know a word is the subject of a sentence, then it needs to take nominative case.
To know if a noun (person, place, or thing) is the subject of the sentence (and takes nominative case), ask the questions Who? or What? is being talked about in the sentence.
In Bosnian: Ko? (Who?) or Šta? (What?)
💡 Think of the nominative as the "dictionary form" of words - it's how you'll find them in a dictionary!