Starting with a preposition is a simple way of changing the start of a sentence. It adds details to the main clause that follows.
Prepositions can be very simple, or can be a longer, more detailed explanation.
Examples of Starting a Sentence with a Preposition Phrase
Behind the last house on the left, the boys played football.
Above the clouds, in the clear azure sky, the plane flew.
In front of the old school, where he had studied so hard but learnt so little, Dave cried.
With her hair blowing in the wind, she drove the car out of town.