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'.)

A Complex Sentence has one main clause and one or more Subordinate Clauses.The main clause or Principal clause makes complete sense by itself and does not need other clause for its complete meaning. It is, thus, of an independent nature. But the Subordinate clauses depend on the principal clause for their meaning. For instance, in
    The President said | that he believed in women education
      (Principal clause)                          (Subordinate clause)
The principal clause makes complete sense by itself but the subordinate clause does not.
Co-ordinate clauses are those which are complete sentences in themselves,that is,they have a subject and a finite verb of their own, but are a part of a large sentence joined by the co-ordinate conjunction. For instance,in
    The path was well lighted and we could see our way.
both the parts contain a subject and a predicate of their own ie, Principal or Main clause. Each par is, therefore,a sentence which is part of a large sentence. In other words, each part is a clause joined by a co-ordinate conjunction and, So it is a Co-ordinate clause.
Thus, a clause is a group of  words which forms part of a larger sentence and has a subject and a verb.
2. Clauses - kinds
    Clauses are of the three kinds :
         (a) Principal or main clause
         (b) Subordinate or Dependent clause
         (c) Co-ordinate clause
3. Subordinate clauses - kinds
   Subordinate or Dependent clauses are of four kinds. There are:
(a)The Noun clause which does the work of a Noun.
           All know that he is a qualified doctor.
that he is a qualified doctor is the subject of the verb know and also does the work of an object of this verb also. Here it does the work of a noun. So it is a Noun clause.
(b) The Adjective Clause which does the work of an adjective.
          This is the boy who met us yesterday on the road.
who met us yesterday on the road tells us about the boy and it, therefore,does the work of an adjective.It is, therefore, an Adjectival clause.
(c)The Adverb clause which does the work of an Adverb.
       I met my old student when i went to the bank.
when I went to the bank qualifies the verb and it does the work of an Adverb here. It is, therefore, an Adverbial clause.
(d)The Non-finite clause contains a participle or an infinitive (a non-finite) but no finite verb.
             My mother went to market to buy fruits.
to buys fruits is a non-finite verb.So this clause is called a Non-finite clause.