Once a 3D model has been created, you can add a scale to it. This scale sets up the model so that it is correctly dimensioned.
Besides adding a scale, you may wish to place the model in a particular orientation. For example, you might want the bottom of the object to lie on the XY plane so it fits with your other CAD work.
See the Importing and Setting Up Coordinate Systems section for details on adding scale and a coordinate system to your model.