Here are some examples:
* On the table sat a vase of flowers.
* In the garden bloomed a beautiful rose.
* With a smile he greeted his friend.
In these examples, the prepositional phrases (on the table, in the garden, with a smile) describe the noun that follows them (vase, rose, he).
Note: While prepositional phrases can modify nouns, they can also modify verbs, adjectives, and other adverbs.