Which value to use for tag_id to create EntityTag
A few advices :


when you chain, you shouldn't have to define the entity_table. If you want to define it anyway, the entity_table should be the database table - i.e. civicrm_contact in your case.
Label and id of the tag can be used in tag_id but i really encourage you to use the id. The label can change or be language dependent while the id could not change.


But to answer your question, in your case, the real problem is the array part. The EntityTag api is to create one tag assignation. I don't think there is a syntax to assign multiple tag.

It could be nice to be able to add several api.EntityTag.create but because the key is the api call definition, it's impossible right now (or i don't know how).

So while this will work fine :

$result = civicrm_api3('Contact', 'create', array(
  'contact_type' =&gt; "Individual",
  'first_name' =&gt; "xxx",
  'last_name' =&gt; "yyy",
  'api.EntityTag.create' =&gt; array('tag_id' =&gt; 5),
));


If you have multiple tags, i suggest you do :

$result = civicrm_api3('Contact', 'create', array(
  'contact_type' =&gt; "Individual",
  'first_name' =&gt; "xxx",
  'last_name' =&gt; "yyy",
));
$contact_id = $result['id'];
foreach ($tags as $tag_id) {
  civicrm_api3('EntityTag', 'create', array(
    'entity_table' =&gt; 'civicrm_contact',
    'entity_id' =&gt; $contact_id,
    'tag_id' =&gt; $tag_id,
  );
}


EDIT

For multiple tags, you could try (not tested but work for website for example - https://github.com/civicrm/civicrm-core/blob/master/api/v3/examples/Contact/ChainTwoWebsites.php)

$result = civicrm_api3('Contact', 'create', array(
  'contact_type' =&gt; "Individual",
  'first_name' =&gt; "xxx",
  'last_name' =&gt; "yyy",
  'api.EntityTag.create' =&gt; array('tag_id' =&gt; 5),
  'api.EntityTag.create.2' =&gt; array('tag_id' =&gt; 8),
));