They're typically not used in Latin verb conjugations. In English, we say, "I love," "you love," "he loves"; we like to speak the personal pronouns that go with the conjugated verb. But in Latin, as in modern Spanish and Italian, subject pronouns were usually omitted, except where the speaker meant to emphasize them. Thus, the everyday verb conjugation above would have this well-known configuration: amo, amas, amat. For the ancient Latin speaker, the personal pronoun as subject was repetitive. The conjugation of the verb was enough to indicate person, number and gender. And so when a personal pronoun is placed in the nominative, it emphasizes the subject; however, the personal pronoun is used regularly in all other cases and functions.
**Besides the nominative singular, most forms of the interrogative pronoun are identical to the relative pronoun. The nominative singular, however, is "quis" in the Masc/Fem and "quid" in the neuter. Additionally, there are no separate feminine forms for the accusative and ablative singular.