How to extend a function I am new to Drupal. Learning Drupal 8. I am little aware of "hooks", but I am little confused.

For example, I have installed Rate module. 

Now, I am trying to do more things based on user's action on RATE, whether vote up/down?

On each vote up/down, add some more details on Node and reward/penalise the node author.

I have tried doing: in my my_module.module file

function my_module_vote_rate_vote_alter($vote, $context) {
    drupal_set_message(t('called '), 'error');
}


But this does not display message.

I know this is third party extension. 

But I am more interested in how to know, which alter/hook method I can use within the module/drupal.
I'm not seeing any hook named hook_vote_rate_vote_alter(), and the Drupal 8 version of the module is in development still. Your problem may be there.