Modify existing custom content form I'm very new to Drupal development and I am completely stuck(.

I have a custom content form, where I need to hide some fields in Inline Entity Form.
I am trying to write my own custom module to achieve this, I am doing the following:
1. I create module folder, where I put info.yml file
2. I create Controller file, where I add custom class and this code inside this class:  

public function MY_MODULE_form_alter(&amp;$form, FormStateInterface $form_state, $form_id) {if ($form_id == 'MY_FORM') {...};



The next thing I am completely stuck at is do I need a routing file to make this work?
I can't find any info about this so I'd really appreciate some help!
And if I need routing, what should I write there?
Thank you very much! 
I really didn't need routing! 

Well, finally I found the solution to my problem - I created the module with 2 files only - mymodule.info.yml and mymodule.module.
In .module file I only added these lines of code and everything worked! (Almost)

function mymodule_inline_entity_form_entity_form_alter(&amp;$entity_form, &amp;$form_state) { 
if ($entity_form['#entity_type'] == 'node' &amp;&amp; $entity_form['#bundle'] == 'my_custom_content_type_machine_name') { 
  unset($entity_form['field_I_need_to_hide']); 
}}