Here's why:
* Prepositional phrases start with a preposition and end with a noun or pronoun (called the object of the preposition).
* Prepositions are words that show the relationship between a noun or pronoun and another word in the sentence.
Examples:
* In the garden (preposition: in, object: garden)
* On the table (preposition: on, object: table)
* With my friends (preposition: with, object: friends)