Relative pronouns are words which are used to give extra information. These words are which, who, whose, where, when, why, and that. These words are placed in front of adjective and adverb clauses, for example:
The book that she wrote was the best-seller.
He's the man whose car was stolen last week.
Winny will tell you what you need to know.
The head coach will select whomever he pleases.
The dog which was lost has been found.