Imagine if you were climbing up a ladder and there were no wall or support holding the ladder up. That's what cantilevered stairs are like in a way.
These stairs have steps that stick out from the wall or the floor without any visible support underneath or beside them. How come they don't fall off? That's because the steps are attached to a strong metal or wooden beam that's hidden inside the wall or the floor.
To put it in simpler terms, the cantilevered stairs are like a magic trick where you're not supposed to see what's making it work. But rest assured that there's a whole lot of engineering and planning involved to make sure the steps stay up and safe to use.