Here are the common relative pronouns:
* who (refers to people)
* whom (refers to people, used as the object of a verb or preposition)
* whose (shows possession)
* which (refers to things)
* that (refers to both people and things)
Example:
* The woman who lives next door is a doctor. (Who refers to "woman")
* The book that I borrowed is very interesting. (That refers to "book")
* The car, whose engine is broken, is being towed away. (Whose refers to "car")
Let me know if you'd like more examples or want to explore relative clauses in more detail!