Logichook writing issue

Hi, I want to run logichook after creating case and then selecting user from the given below users module option.
I have no clue of what to write in logichook file to execute my code. I don’t know about more terms of it but i think it may match with after save relationship.

Do you need help in writing Logic hooks?
Or you looking help in finding which logic hook work for you?

I need help in finding which logic hook work for me?