If that's what you're referring to, foundations are in the build mode and have to be placed down before walls. You click on the part of the house in build mode labeled foundations, porches and platforms under where you click on floor tiles and place it in the shape you want the house.
It will come out brick colored and you have to paint it to make the house. Stairs will connect to a foundation but there has to be two squares of space for a door and stairs to lead towards one another.
There is even a diagonal foundation tool for more looks.
Finished result:
Is that what you were talking about?
