EDIT: I mistakenly made this post thinking you were talking about making arced shapes on a flat plane. Sorry for the misunderstanding.
Hi, I'm also a newb, but what I ended up doing to make sure my 'freeform' drawings were on the same plane is the following:
Make a plane of any size, large enough for the shape you want to make to fit inside,
make the plane a group (so lines drawn on it don't attach to the plane)
draw your shape on the surface of the plane,
when you connect the last point, the surface should automatically come into being like magic.
delete your drawing surface plane (or throw it off to the side and save it for later)
Again, may not be the best or most efficient way to do it, but it works for me.
