How to delete all Taxonomy terms of particular vocabulary using entity_delete_multiple?
Try to use vid instead of type. I haven't tried the code, but try the following 

$result = \Drupal::entityQuery('taxonomy_term')
      -&gt;condition('vid', 'tags')
      -&gt;execute();
  entity_delete_multiple('taxonomy_term', $result);


Here is a good example for using entityQuery.

For deleting users, you can use entity_delete_multiple or user_delete_multiple

To delete user with uid 10

entity_delete_multiple('user', \Drupal::entityQuery('user')-&gt;condition('uid', '10', '=')-&gt;execute());


or pass an array of uids to user_delete_multiple

user_delete_multiple(array $uids);


I'm not aware of how to delete comments.