create 3d model at runtime

I can create object at the runtime for example ‘Cube’

var cube : GameObject = GameObject.CreatePrimitive(PrimitiveType.Cube);
cube.transform.localScale = Vector3(2.036378F, 8.689441F, 3.935793F);
cube.transform.position = Vector3(1.502899F, 3.888695F, zaxis);

But i want to create 3d model in a downloaded to unity asset store.
How can i do it ?

You can save your downloaded 3d object as prefab, and Instantiate it when you need it