PREPOSITION
A preposition connects words, clauses, and sentences together and shows the relation between them. "My hand is on the table" shows relation between hand and table.
Prepositions are so called because they are generally placed before the words whose connection or relation with other words they point out.
CONJUNCTION
A conjunction joins words, clauses and sentences; as "John and James." "My father and mother have come, but I have not seen them."
The conjunctions in most general use are and, also; either, or; neither, nor; though, yet; but, however; for, that; because, since; therefore, wherefore, then; if, unless, lest.
INTERJECTION
An interjection is a word used to express some sudden emotion of the mind. Thus in the examples,—"Ah! there he comes; alas! what shall I do?" ah, expresses surprise, and alas, distress.
Nouns, adjectives, verbs and adverbs become interjections when they are uttered as exclamations, as, nonsense! strange! hail! away! etc.
We have now enumerated the parts of speech and as briefly as possible stated the functions of each. As they all belong to the same family they are related to one another but some are in closer affinity than others. To point out the exact relationship and the dependency of one word on another is called parsing and in order that every etymological connection may be distinctly understood a brief resume of the foregoing essentials is here given: