First, what are the sentences that you need to analyze?
Nominative case pronouns are I, you, he, she, it, we, they, who, whoever.
They are the SUBJECTS of sentences, or the doers of the actions. Pronouns take the place of nouns, and when a pronoun takes the place of a noun in the subject of a sentence it is in the nominative case. Nominative case pronouns DO things. They always tell who or what acted in the sentence because they are the subject of the sentence.
*HINT: the root 'nom' in the word nominative means 'to name', so think of the pronoun naming the doer of the action.
Examples:
I went to the grocery store. (I is the nominative pronoun and the subject of the sentence, went is the verb. I names who went to the store.)
Are they going to go to the store this morning? (THEY is the nominative pronoun and the subject of the sentence, are going is the verb. You names who is going to the store.)
You must think that John loves cookies! (YOU is the nominative pronoun and the subject of the sentence, must think is the verb. You names what person loves cookies.)
Whoever decides on a book had better choose a good one for book club! (WHOEVER is the nominative pronoun and the subject of the sentence, decides is the verb. Whoever names who decides on a book.)
We sang a song to the children. (WE is the nominative pronoun and the subject of the sentence, sang is the verb. We names who sang a song to the children.)