The number of steps is automatically calculated from the floor to ceiling height and the values that you may have edited in the stair dialog for tread depth and height.
Some possible causes of error:
You should add the stairs from ground floor to first floor actually on the ground floor. Ensure that you have your next floor added to ensure that the calculation works. This is likely to be the cause of your problem especially if you are adding the stairs in a 3D view. So its always best to add in a 2D view.
You may have unchecked Automatic positioning above construction in the stair dialog.
You may have an incorrect value in your floor to ceiling height.
Sorry that the image you tried to upload did not upload, but if you email us the project with the stair problem we can advise you.
The following tutorial video is an introduction in the use of the stair tool:
See also the more advanced tutorial on how to add a wall below a stair:
