Recipe and best practice for accessing COM

[newToCOM]

I am trying to use COM to access Windows functionality and APIs.
I have read the interface documentation and some documentation at
MSDN. I have seen the included sample snippet for IHello and the
slides "Modern COM programming in D", but it is still not clear
exactly what to do and what the best practice is.

So, my question is:
I have downloaded Windows SDK and coffimplib. How do I proceed to
access d2d1 and draw a rectangle?

A stepwise description of the recommended procedure is highly
appreciated!