Are you asking what “Z wave direct association“ is? That seems to be a question that would go with the post that you linked to, but it doesn’t match the title that you gave to this thread. So I’m rather confused.
A device type handler is required for every device which is used with SmartThings. It’s like a printer driver: it’s just a bit of code which tells smartthings how to format the instructions that that device will expect.
Why don’t you start by reading the custom code FAQ and see if that clears up anything For you. After that we can see if we can figure out what your more specific question is.