To superpose means to place something on top of something else.
Superposed things are on top of each other, like when you put one toy on top of another.
Examples:
I will superpose the red block on top of the blue block.
She superposed the plate on the table.
The cat superposed itself on the dog.
I superposed the hat on top of my head.
He superposed the books on the shelf so high!
The superhero superposed himself on the villain to catch him.