What is the difference between Tag or Group
both tags and groups are ways to segment contacts. There are a few differences:

Tags
 - can be used for contacts, activities, cases and attachments
 - quick to add, easy to use and find
 - you can not extends tags with custom fields AFAIK
 - easy to spot on the contact summary (if you do not use too many)
 - can not be used to create a segment of contacts for a bulk mailing

Groups


can be used to segment contacts only
can be extended with custom fields
can be used for Bulk Mailing and ACL's (fine grained permissions), scheduled reminders and subscribe/unsubscribe
you can also create smart groups (check https://docs.civicrm.org/user/en/latest/organising-your-data/smart-groups/)


You can read a little more on https://docs.civicrm.org/user/en/latest/organising-your-data/groups-and-tags/ and I would recommend you play a little with both to discover what would be the best alternative for your specific need.

And a little remark at the end: although there is a CiviCRM Core Team most of the posts on this forum are answered by community members :-) I get the impression from the "Civi-Team" you are expecting a big team of people employed by CiviCRM answering these questions :-)