Staircases are sets of steps that you walk up or down to go between different levels of a building.
Staircases are usually necessary in buildings with more than one floor.
Examples:
She walks up the staircase to her bedroom.
The staircase in the library is very long.
He runs down the staircase to catch the bus.
The cat sits on the staircase and watches everyone.
The staircase in the castle is so big, it takes a long time to climb it.
I always count the steps on the staircase when I go up.