Pronouns such as I, we, you, he, she, it, and they are used to take the place of nouns in sentences. They refer to the speaker, the person spoken to, or the person spoken about. These pronouns are called subject pronouns because each is used as the subject of a sentence, as shown in the examples of "We are present today" and "You and I are best of friends." Further examples demonstrate the use of subject pronouns like it, she, we, he, and they to replace nouns and act as subjects.