Snapping to Ground - 123D Design
The position matters a lot if you use the default STL file without doing anything in the slicer.  I've used 123D extensively and when I've inadvertently left a gap between the part and bed (and not snapped it to the bed in the slicer), the printer tries to print in mid air.  Use "d" to "drop" the object to the grid.  Different slicers have similar commands that will attach a face to the bed.  I use Simplify3D.