Look at the following sentences
(a) He is honest and she is intelligent.
(b) I shall either read or write a book.
(c) Three and three make six.
(d) Suresh and Ganesh are friends.

वाक्य (a) एवं वाक्य (b) में Conjunction 'and' एवं 'or' दो वाक्यों को जोड़ने का कार्य कर रहे हैं, जबकि वाक्य (c) एवं (d) में Conjunction 'and' दो शब्दों को जोड़ने का कार्य कर रहा हैं।

Conjunctions are words that join clauses together to make sentences, and show how the meanings of the clauses relate to each other.

Kinds of Conjunction

Conjunctions को निम्नलिखित तीन भागों में वर्गीकृत किया गया है

1. Coordinating Conjunction.
2. Subordinating Conjunction.
3. Correlative Conjunction.

 1.  Coordinating Conjunction

ये Conjunctions दो समान Rank के Sentences या Words को जोड़ते हैं। इस तरह के मुख्य Conjunctions है: For, and, nor, but, or, yet, so. An easy way to remember these six conjunctions is to think of the word FANBOYS. Each of the letters in this somewhat unlikely word is the first letter of one of the Coordinating Conjunctions.

इन Conjunctions द्वारा एक Subordinating Clause को अन्य Clause से जोड़ा जाता है। (Subordinating Clause) वह है जो अपने पूर्ण अर्थ के लिए अन्य Clause पर निर्भर होती है। इस तरह के मुख्य Conjunctions: after, although, as, as if, as long as, as though, because, before, even if, even though, if, if only, in order that, now that, once, rather than, since, so that, than that, though, till, unless, until, when, whenever, where, whereas, wherever, while.

NOTE
Note that some of the Subordinating Conjunctions in the above examples like: after. before, since are also prepositions, but as Subordinate Conjunctions, they are being used to introduce a clause and to subordinate the following clause to the independent element in the sentence.

Examples:
After:
We are going out to eat after we finish our work.
After the rain stopped, the dog ran into the mud to play.

Since:
Since we have lived in Mexico, we have gone to every exhibit at the Royal Hall.

While:
While I was waiting in line for my turn, I ate my lunch.
Shalini steamed the com while Jack fried the steaks.

Although:
Although the line was long and the wait over at least three hours, the exhibit was indeed worth it.

Even if you have already bought your ticket, you will still need to wait in a queue.

I love her work because she uses color so brilliantly.
The snowman melted because the sun came out.

Even though Jack fell asleep, the mobile salesman kept talking.
(C) Correlative Conjunction: जो Conjunctions जोड़े (pairs) में प्रयोग किए जाते हैं, उन्हें Correlative Conjunction कहते है.। जैसे: Either...or, Neither .nor, Both..and, Whether.. or, Not only. .but also.

Remember
Correlative Conjunctions are always used in pairs. They join similar elements. When joining singular and plural subjects, the subject closest to the verb determines whether the verb is singular or plural.

Important
Coordinating Conjunctions are the simplest kind, and they denote equality of relationship between the ideas they join. Their relatives, Correlative Conjunctions, not only denote equality, but they also make the joining tighter and more emphatic.
Coordinating and Correlative Conjunctions are great when two ideas are of the same importance, but many times one idea is more important than another Subordinating Conjunctions are used to show which idea is more and which is less important. The idea in the main clause is the more important, while the idea in the subordinate clause (made subordinate by the Subordinating conjunction) is less important. The subordinate clause supplies a time, reason, condition, and so on for the main clause.

Conjunctive Adverbs

Conjunctive Adverbs make up an even stronger category of Conjunctions. They show logical relationships between two independent sentences, between sections of paragraphs, or between entire paragraphs. Conjunctive Adverbs are so emphatic that they should be used sparingly; however, when used appropriately, they can be quite effective.

Such Conjunctive Adverbs are: Also, hence, however, still, likewise, otherwise, therefore, conversely, rather, consequently, furthermore, nevertheless, instead, moreover, then, thus, meanwhile, accordingly. 

Examples:
If the salmon is grilled, I will have that; otherwise, I might have the chicken.
James has a garage full of woodworking tools. He might, however, have some metric wrenches. too
I do not recommend that you play with a stick of dynamite lit at both ends. Rather, a ham sandwich would be better for you.

Expletives

Expletives are closely related to conjunctive adverbs. Expletives convey no meaning of their own but instead serve only to emphasize the statement to which they are attached. As such, then, they technically do not show a logical relationship like time or cause between ideas, and that fact prevents them from being treated as conjunctive adverbs.

Such Expletives are: Of course, indeed, naturally, after all, in short, I hope, at least, remarkably, in fact, on the whole, I suppose, it seems, in brief, I think, clearly, assuredly, definitely to be sure, without doubt, for all that, in any event, importantly, certainly.

Conjunction/Relative Pronoun/Relative Adverb/Preposition

Conjunctions का कार्य मात्र वाक्यों या शब्दों को जोड़ना है, जबकि Relative Pronoun/Relative Adverb/Preposition न केवल Pronoun या Adverb या Preposition का भी कार्य करते हैं, बल्कि वाक्यो को जोड़ते भी हैं।

Look at the following sentences
(a) This is the pen that she gifted me. (Relative Pronoun)
(b) This the place where I was born. (Relative Adverb)
(c) He sat beside Shyam. (Preposition)
(d) He came and he worked. (Conjunction)

वाक्य (a) में 'that' Noun, pen को भी Refer कर रहा है एवं दो वाक्यों को जोड़ भी रहा है। इसी तरह वाक्य (b) एवं (c) में Underlined words. Adverb एवं Preposition का कार्य कर रहे हैं एवं दो वाक्यों को जोड़ भी रहे हैं, जबकि वाक्य (d) में Conjunction मात्र दो वाक्यों को जोड़ने का कार्य कर रहा है।