When you deploy a project REFramework there is a documentation.
Also I read here:
But I can’t understand the difference between them in REFramework.
I think both of them they make the same result, for example if I need to close NAV Client, I can do it with both of them. But If I want to be sure he is completely close I will use KillAllApplications(Kill Process activity) Instead of CloseAllApplications (Close Application activity)