How does a staircase construction work? What supports the staircase?

[stalf]

Very broad and general question, but I'm curious about how a staircase actually works. Yes, it has steps that allow one to go up and down, that part I understand

I'm wondering about how the construction works. A typical straight or L-shaped staircase found in almost every house, how is it supported? How is it attached?

 

[oddjobb]

The vangstycken, on both sides, are those which are attached to the wall, post, or rest on the floor.