Every sentence has a
verb and a
noun.
The relative clause starts with a relative pronoun: who, whom, whose, that, or which.
Who for people The lady who I helped thanked me.
Which for animals and things The computer which I bought yesterday broke down.
That for people, animals and things Here is the hat that I bought in New York.
Whom who + preposition I was invited by the professor whom I met at the
conference.
Whose for possession Do you know the boy whose mother is a nurse?