The man who sold you an expensive car is a good salesman.
Here's how it works:
* "The man" is the main subject of the sentence.
* "who sold you an expensive car" is the relative clause. It modifies the noun "man" and provides more information about him.
* "who" is the relative pronoun that connects the relative clause to the main clause.
* "is a good salesman" is the predicate of the sentence, telling us something about the man.