Here are some groups of prepositions. They all show the position of an object.
after and before:
I’ll pick you up after school.
Sara went for a walk after dinner.
Be sure to come home before dark.
We will talk before the game.
above and below:
The bird flew above the trees.
Mom hung the poster above my bed.
I put my books below the counter.
The band sat below the stage.
across and around:
We walked across the bridge.
The truck drove across the parking lot.
The teacher walked around the room.
I drew a line around my answer.
Prepositions always show the position of an object. Prepositions are always the first word of a prepositional phrase. The object of the preposition is at the end of the phrase.