animated rig - why aren't the joints limited in movement?

ok so first let me say I'm VERY new to animations etc in Unity. I come from software development background.

With that said, I downloaded some basic animations pack (https://www.assetstore.unity3d.com/en/#!/content/26680), created an instance of the character given with the pack, created an animator controller of my own for it, and used the imported animations.

So far so good, everything works.

Now I'm trying to add my own animations on the model. I see there's the character model, which is a single mesh, and a node called Root under which there's an hierarchy of nodes which I presume is the avatar of the character.

So I created a new animation, but when I move the different parts of the character, for example the hand, it doesn't act like its connected to any skeleton at all. moving the avatar nodes just more the mesh parts connected to it, but it does not limit my movement like with a skeleton and it doesn't affect any other parts. And its really hard to animate anything like that.

What I expect to happen is that if I pull the hand forward, the entire arm will be pull and rotated with it, based on joints. But I'm not even sure this model comes with such a thing.

Anyway can someone give me a hint or directions to what I'm doing wrong and how I'm suppose to do it?

Thanks!