For example in the user module there is a hook_user_login
hook
When a user logs in in function user_login_finalize()
will be called, then user_login_finalize
will call user_module_invoke('login', $edit, $user)
;
that will call system_user_login
(and others module's function[moudulename_user_login
] that implements hook_user_login()
);
I am puzzled at which function will call hook_user_login()
and when it will be Invoked. What is the role of this function?