Noun Clauses are dependent clauses that function as nouns, which means they can perform any function that a noun can.
Noun clauses are usually introduced by that, what, who, whom, whatever, whoever, whomever, whether, which, whose, when, where, why.
Examples of the noun clause used as…
Subject: Whatever you cook is fine.
Direct Object: We found what you needed.
Indirect Object: You should give whoever is most deserving the money.
Predicate Nominative: That is who will win the championship.
Object of Preposition: Be thankful for what you have.
(See more examples in The Writing Guide "Using Clauses" Section)