How to set "target" for Custom Properties?

[Alexx31]

Hello, I solved my original question, so this question is edited:

I wonder, how I can work with "targets" in the custom properties operator.
In the attached scene I was trying to use the targets.

(It worked with "self" after some adjusting)

There is the option to "Set" Values as target.
I did not find something detailed in the documentation.

It would be great if someone could explain.
Thanks