A preposition is a word that comes in front of a noun or a pronoun and shows a connection between that noun or pronoun and some other word in the sentence.
The preposition is said to govern the noun or pronoun it comes in front of. In a way, the preposition controls the noun or pronoun after it. The noun or pronoun cannot get away from the preposition. Remember that when you start learning about sentences.
Example: The bird flew over the water.
Over is a preposition governing the noun water. It establishes the connection between water and the verb flew.
The word group over the water is a prepositional phrase. The words are, in a sense, stuck together: over-the-water. Here the prepositional phrase functions like an adverb, telling where the bird flew.
Words commonly used as prepositions are: above, across, after, at, before, behind, below, for, from, in, inside, into, through, to, toward, towards, under, with, and within
REMEMBER: A word does not become a part of speech until it is used in a sentence. Many of these words can also be used as different parts of speech, such as adverbs and conjunctions. To function as a preposition, the word must be followed by a noun or pronoun that acts as its object.