Only handles can be created of a managed class. Why?

Hi

I am beginner for Visual C++ and currently just learning the concepts of it.

I came to know that there are 2 classes: Managed class & Value class.

1) Value classes are like normal C++ class, whose objects can be created which will hold the data.

2) Managed classes are memory managed by garbage collector. But their objects can't be created only handles can be created. Why???

& Also please give me brief idea about that is instance? Is it just an object creation or something else?

Thanks