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?

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.