How can I hook into entityforms being submitted? I've installed entity forms. I have made a form. I would like to fire some code when a user fills out and submits the form I have created. I do not know how to do this. I don't know which hook to use, nor entirely understand how hooks work.

I've done my best to learn php and read the documentation, but I don't understand. I understand that this is likely a very simple question, I have never had any formal computer training, so even the simplest concepts allude me.
Entityforms are - as the name suggests - stored as entities. So you can hook into hook_entity_insert(), or hook_ENTITY_TYPE_insert(), having the inserted data as parameter (the entity will be an object):

/**
 * Implements hook_entity_insert().
 */
function MYMODULE_entity_insert($entity, $type) {
  if ($type == 'entityform') {
    // Do your stuff here.
  }
}


or

/**
 * Implements hook_ENTITY_TYPE_insert().
 */
function MYMODULE_entityform_insert($entityform) {
  // Do your stuff here.
}


You could also utilize rules to define custom actions on submission, as the entityform submission triggers the entityform_submission rule.