A. The Noun Clause
     1.The Noun Clause does the work of a noun in a complex sentence. Different kinds of noun clauses are introduced by that or the question-words like, why, where, when, what, who, how etc.
They can also be introduced by if or whether. These can be :
     (a) Noun clause the subject of a verb
           What the President said  was true.(what the President said is the subject of the verb 'was'.)
           It was true main clause in this sentence 
           How he could help us was not known.
                 Noun Clause     
           It was not known
               Main Clause
  (b)Object of a verb
         I know where he has gone.
          (I know is main clause as noun clause answers the question WHAT
          where he has gone is a noun clause object of the verb know
        Ask if her father is at home.
         Ask is main clause here and if her father is at home is a noun clause object of the verb ask.
(c) Object of a preposition
        Pay attention to what he is going to say.(The noun clause is governed by the preposition 'to' in the Principal clause.)
        Be careful about what your teacher said.
           Main Clause            Noun Clause
(d) The Complement of a verb of incomplete prediction.
       My wish is that he may pass. (That he may pass is the complement of verb 'is' of the principal clause.)
       Life is what you make it.
          MC             NC
(e) In apposition to noun or pronoun
    your statement that Anuradha is guilty will not be believed. (that Anuradha is guilty is in                                                                                                       apposition to the noun to the noun 'statement'.
(f)As the object of an infinitive
    I feel happy to know that you have come.(that you have come is the object of the infintive 'to know').
(g) As the object of a participle
      He left the house saying that he will never return.(that he will never return is the object of the participle'saying'.)