A preposition phrase says where a noun is.
Each Saturday I go to the football field which sits behind the school.
A simple way to vary sentence patterns is to put the preposition first.
Behind the school sits the football field to which I go every Saturday.
Prepositions can be very simple, or can be a longer, more detailed explanation.
Examples
Behind the last house on the left, the boys played baseball.
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.