Can you provide a screenshot of your floating issue please.
Also does this happen after you apply a pose to the figure?
Ground plane you can either use one that comes with content or use a Primative, Create > New Primative and select a Plane, give it a size and divisions and accept. You will then have to texture the plane yourself but that is easy, via the Surfaces Pane. If you don’t know how then we will have to find a tut or walk you through it but trust me it is very easy.