"Stairs" can't easily be counted, but here are ways that you can specifically count them:

• One whole set of stairs in a building is called a "staircase". Most buildings only have one staircase, but some large buildings might have 2 or 3 separate staircases.
• One "flight of stairs" connects two floors. For example, between the ground floor and the 2nd floor is one flight of stairs; between the 2nd and 3rd floor is another flight, and so on. There can be several flights of stairs in one staircase.
• Sometimes there will be a "landing" halfway up a flight of stairs. This is a wider area where the stairs turn around and go in another direction.
• A staircase or a flight of stairs is made up of lots of "steps". You usually walk up one step at a time.