Subject pronouns are words that replace nouns in a sentence and indicate who is performing the action. Common subject pronouns include I, you, he, she, it, we, and they. These pronouns help avoid repetition and make sentences clearer. For example, instead of saying "John is going to the store. John will buy milk," you can say "He is going to the store. He will buy milk." Using subject pronouns correctly is essential for proper grammar. They agree in number and gender with the nouns they replace. For instance, use he for a male subject and she for a female subject. In plural forms, we refers to a group that includes the speaker, while they refers to a group that does not.