A conjunction is a word or a phrase used to join words, phrases or classes. Let us take this sentence; I am late because I could not get a taxi. In this sentence, there are two parts (clauses) “I am late” and “I could not get a taxi,” the word “because” joins the two parts together. Let us take another example: He is not intelligent, but he works very hard. In this sentence the first clause is ‘He is not intelligent’ and the second clause is ‘he works very hard’. The word ‘But’ joins the two parts together and will be called Conjunction. Sometimes a Conjunction is used right in the beginning of a sentence. For example we say, “He listened to me patiently though he was angry”. The same sentence can be written as, “Though he was angry, he listened to me patiently”. In both these sentences the Conjunction ‘though’ performs the same function.

Kinds of Conjunctions

            Conjunctions are of two kinds.

Co-Ordinative Conjunctions

These are the Conjunctions which either join those parts of sentence which are equal co-ordinating rank or words that stand in the same relation to some other word in the sentence. Some of the examples of Co-coordinative Conjunctions are:-
And, both, but, either-or, neither-nor, as well as, otherwise, still, yet, but, for, therefore, consequently, nevertheless, moreover etc.

Sub-Ordinative Conjunctions

These are the Conjunctions which join Principal clause to
        subordinate clause. Some of the examples are:-
             That, after, till, since, because, if, unless, except, though, whether
             and where etc.