How to create own shapes with connections?

[zweiund40 <thoswald42 gmail com>]

Hi. I'm trying to create a new shape with connection points and it's 
driving me crazy. It doesn't work. But on the other hand there are many 
other shapes per default in dia and all of them are provided with 
connection points. I wonder why all my efforts fail. There must be a way 
to do it. But how? Is there anyone who knows how it works?

Best wishes