Hi Macario, hope I'm not too late with the answer and that it's still useful to you, but in the fundamentals of rigging course you'll learn how to make these handles :)
I second that. As a quick answer though, you can set bones to use arbitrary meshes for display. All bones have a display section where you can use the eyedropper to specify a mesh. Additionally while a bone is selected you can lock the properties that can change in the "Transform Locks" section of the Bone panel. The rotation bone in this rig has everything but rotation locked for example.
If you want to know more I suggest that you go through the rigging fundamentals course and try to reverse engineer the rig in the example. Having done so myself I wrote a breakdown of how the rig was made. Feel free to ignore the rest of the answer as it got a bit long.
The rig used in this consists of 4 bones. The parent hierarchy goes
Location Bone -> (Squash Upper and Squash Lower)
Squash Lower -> Rotation
The ball's deformation is controlled entirely by the Rotation bone, but the rotation bones is a child of 2 other bones so the scale and orientation can be affect by any parent bones.
Squash Upper can also indirectly affect the rotation bone through Squash Lower (Rotation's parent). Squash Lower has a bone constraint of type "Stretch To" with Squash Upper set as the target. This makes it so the tail of Squash Lower attaches to Squash Upper even though there is no direct parent child relationship.
One last note. The parenting of the mesh to the rig appears to be slightly different than what is taught in the rigging fundamentals course. If you look at the modifiers panel of the mesh you will notice that there is no Armature modifier. I believe that this is because the mesh is parented directly to the Rotation bone. However, there is still a tiny bit I do not understand.