Noun Clauses

What Are Noun Clauses? 
A noun clause is a clause that plays the role of a noun. For example (noun clauses in red):
I like what I see.
I know that the tide is turning.
I've met the man who won the lottery.

Compare the three examples above to these:
I like cakes.
I know London.
I've met Madonna.

The words in blue are all nouns. This shows that clauses in red in the first three examples are functioning as nouns, making them noun clauses.

Another example:

The "empanada" gave me heartburn.

("empanada" and "heartburn" are the nouns in this sentence. "Gave" is the verb and "empanada" is the subject.)

But What About This One?

What I had for breakfast gave me heartburn.

(The verb is still "gave," but the subject is a noun clause: "What I had for breakfast.")

Like any noun, a noun clause can be a subject, an object, or a complement.
In a sentence, a noun clause will be a dependent clause. In other words, a noun clause does not stand alone as a complete thought.

Examples of Noun Clauses:
-A person who trusts no one can't be trusted. (This noun clause is the subject of the sentence.)

-That he believes his own story is remarkable. (This noun clause is the subject of the sentence. Be aware that starting a sentence with a noun clause starting That is acceptable, but it grates on lots of people's ears. As a result, many writers prefer to precede it with "The fact…".)

-Ask your child what he wants for dinner only if he's buying. (This noun clause is the direct object of ask.)

-He knows all about art, but he doesn't know what he likes. (This noun clause is the direct object of know.)

-It is even harder for the average ape to believe that he has descended from man. (This noun clause is the direct object of believe.)

-"I never know how much of what I say is true". Bette Midler (This noun clause is an object of a preposition.)

-Man is what he eats. (This noun clause is a subject complement.)

-"My one regret in life is that I am not someone else." Woody Allen (This noun clause is a subject complement.)

Words that introduce noun clauses are:

WHOM, WHOSE, WHO, WHICH, WHAT, WHEN, WHY, HOW, WHERE, THAT


Taken from:
http://www.grammar-monster.com/glossary/noun_clauses.htm