What is a preposition and a prepositional phrase?

Answer 1

My sixth-grade teacher told us an easy way to test if a word is a preposition: See how it sounds when followed by "the desk." In the desk. On the desk. Over the desk. Under the desk. Around the desk. Above the desk. Below the desk. Off the desk.

A prepositional phrase begins with a preposition and ends with the object of the preposition. In the examples above, "desk" is the object.

Answer 2

A preposition is a word that shows the relationship between a noun or pronoun and another word or element in the sentence. It often indicates location, time, direction, or manner. A prepositional phrase consists of a preposition and its object (noun or pronoun) along with any modifiers of that object. It functionally acts as an adverb or adjective in a sentence.