We use personal pronouns (I, you, he, she …) to replace nouns. We use them to refer to people and things that have already been mentioned. They reflect person, number and gender and help us to avoid repetition in our writing. Personal pronouns can be the subject or the object of a sentence, although they have different forms.
The subject of the sentence usually comes at the beginning of the phrase and performs the verb. Logically, we use subject pronouns to replace the subject of the sentence.
Example:
Ms Pearson makes learning English fun. → She makes learning English fun.