The conjunction is a part of speech that denotes connections between objects and phenomena. It connects parts of the sentence, clauses, and sentences.

Sadie brought them in and went back to the door. (Mansfield)

…the blinds were down in the dining-room and the lights turned on — and all the lights were red-roses. (Mansfield)

The other day I was saying to Fabermacher that Haviland isn’t really cruel, he’s just thoughtless. And Fabermacher said that was the cruellest thing about the human race. And he’s right. (Wilson)

According to their morphological structure conjunctions are divided into the following groups:

1. simple conjunctions (and, or, but, till, after, that, so, where, when, etc.). Some of the simple conjunctions are homonymous with prepositions, adverbs, and pronouns.
2. derivative conjunctions (until, unless, etc.).
3. compound conjunctions (however, whereas, wherever, etc.). These conjunctions are few.
4. composite conjunctions (as well as, as long as, in case, for fear (that), on the ground that, for the reason that, etc.).

Some conjunctions are used in pairs (correlatively): both… and, either… or, not only… but (also), neither… nor, whether… or.

If anyone had asked him if he wanted to own her soul, the question would have seemed to him both ridiculous and sentimental. (Galsworthy)

…nor would John Reed have found it out himself; he was not quick either of vision or conception. (Ch. Bronte)

Her son had not only come home, but he had come home a good person. (Abrahams)

Well, they were honest eyes, he concluded, and in them was neither smallness nor meanness. (London)

He was aware of vague memories of rain and wind and snow, but whether he had been beaten by the storm for two days or two weeks he did not know. (London)

As to their function conjunctions fall under two classes:

1. Coordinating Conjunctions
2. Subordinating Conjunctions