A prepositional phrase consists of a preposition as its head, plus the element (noun, noun phrase, or pronoun) functioning as its object. The object of the preposition will often have one or more modifiers to describe it.
1. Preposition + Noun phrase
-She lives at the back of the building.
2. Preposition + noun clause
-From what I have heard, he is not really smart.
3. Preposition + V-ing
-I went home directly after speaking to you.
4. Prepositional + pronoun
You have only to go with me.