Pronouns are words which replace proper (specific, singular) nouns. They make longer, continual conversation or narration smoother by allowing the speaker to not have to repeat the names of people, places and things. For example, in referring to a group of friends, one would use "they" instead of listing all their names (Randy, Laura, Matt and Emily) over and over again. Pronouns are also common in shorter, everyday conversation as well.
We can also divide them into two groups: subject and object pronouns. They get their names from the parts of speech that they replace. Hence, subject pronouns replace subjects (the thing that does the verb) while pronouns replace objects (the thing that the verb is done to). These include:
With proper noun: I am talking about the game with Alice.
With object pronoun: I am talking about the game with her.
With proper noun: Can John, Heather and I go over to the general store?
With subject pronoun: Can we go over to the general store?
With proper noun: Can we go to see the movie later?
With object pronoun: Can we go to see it later?
With proper noun: Has Mr. Presley seen the new business model?
With subject pronoun: Has he seen the new business model?