* Subject pronouns are always used in subject positions. While they are most commonly used in subject positions (e.g., "I went to the store"), they can also be used in other grammatical roles, such as in appositives ("The winner, she, was a surprise") or after certain verbs ("It is me").
* Subject pronouns always refer to people. Subject pronouns can refer to people, animals, or things. For example, "It is raining" or "They are my favorite band."
* Subject pronouns always have the same form. Subject pronouns can change form depending on the number (singular or plural) and person (first, second, or third). For example, "I" is singular first person, while "we" is plural first person.
Let me know if you'd like more clarification on any of these points!