Thanks Mylenium, What about on the bottom right. If you look closely there should be only an arc but its trying to close off the path I think.
I've watched countless pen tutorials and they all say that you can jump back to you project later and contiue adding and removing paths. I must be doing something wrong!
The main part of the screenshot seems to show that the upper left part is a path of its own, selected as opposed to the lower ight part. To fuse it with the lower right part, you may lock what is underneath ((including) the actual staircase) and drag across the top right or bottom left end(s), then Ctrl/Cmd+J to join the paths into one and repeat for the other set to close the path.
Edit: Hi Bill.
I am unsure whether you are thinking of a closed path or an open path (the image in post #4 seems to show just two open paths.
Either way, if I understand it in the right way, you may use Object>Path>Offset Path with the desired distance (setting the number).
For closed paths you will get one closed path outside; to get an inside path at the same distance just use the same negative number.
For an open path you will get a kind of surrounding path with straight end segments through the end Anchor Points. You can Direct Select each of them and delete, and after that you will have one path on either side at the desired distance.