How to use custom trigger?

If you look at the link below, it looks like you can create a custom trigger function.
Please give an example of how to use the function below.

Hi @_dexter - The linked document has steps as to how you can do it. did you try it? if yes what problem do you face if you share might help with resolution?

@ABHIMANYU_THITE1
The linked document is poor.
I don’t know the exact list of packages to refer to.
And when you build the code, it becomes a DLL or package. What is it used for?
I don’t know if this is an activity or something happens automatically.