Prepositional Phrases can be tricky, but don't worry, they are confusing to almost everyone! Below, I have given you some helpful links that will make Prepositional Phrases a little easier to understand.
The first is Prepositional Phrases Help
The second is Grammar Lesson: The Prepositional Phrase
The third is Prepositions and Prepositional Phrases Study Guide
And the last is Prepositions and Prepositional Phrases Practice Exercises which I recommend trying so that you know you understand how to identify a Prepositional Phrase.