A preposition shows the location of an object. These words are prepositions: under, on, inside, in, behind
The toy is under the couch.
The toy is on the table.
The toy is inside the toybox.
The toy is in the closet.
The toy is behind the chair.
In each sentence, the preposition tells where the toy is located.
Notice that each preposition is the start of a prepositional phrase.
under the couch – under is the preposition; couch is the object of the preposition.
The preposition under tells us the location of the toy. The object couch finishes the preposition by telling what the toy is under. under the couch
Use a preposition to tell the location of an object. Remember that a preposition always begins a prepositional phrase.