But I have to explain somehow to the users who know nothing about that terms.

To name the parts of my custom staircases I did a search for "staircase parts diagram". Many results with excellent examples.
Use one of the search results as an example to add names to an image of a generated staircase. Don't use one of the images you find, they might be copyrighted. Display it under a button or in the manual.
(There are some strange names, like 'Kite winder' [:))] )