Looking at the sample scenes, it seems like the MRTK uses a pointer system instead of actually giving you virtual hands that can be manipulated by pressing buttons or triggers on the controllers, and allowing you to grab objects.
Is there a built-in way to use hands?
There is currently not a set of virtual hands build into MRTK for VR, however it would be possible to rig up a custom visual for a controller that looks like hands, and animate the hands based on things like which buttons / triggers are pressed on the controllers.