UITypeEditor working principles

Question

I would like to get a thorough understanding of how does UITypeEditor uses the PropertyGrid to add more functionality to it. I've found some working examples but this does not help much in trying to understand how does it work. I want to use UITypeEditor for the custom-made 3rd party PropertyGrid implementing ICustomTypeDescriptor but it doesn't work.

Any tips or explanations are welcome.

Thanks in advance.