Hi. Doors and windows have to be placed on walls. I saw you used lines for your walls; select them and change the linetype to wall. Why stairs don’t work I don’t know. But I noticed your plan is incredibly large which makes the program react slower than usually. better to limit the amount of plans in one design, but start a new design in the same floor. Also it’s quicker to draw your spaces with the Room tool (1st icon) Then you don’t have to draw floors and walls separately and floors react when you move your walls.

good luck!