I am looking for instructions on how to set up an auto email when someone signs up and joins a specific group. Thank you for your assistance.
Agree with Peter, you can find the CiviRules extension here: https://civicrm.org/extensions/civirules (or in the extensions list when you do Administer>Extension and then click on the Add New tab)
Documentation on how CiviRules work can be found here : https://docs.civicrm.org/civirules/en/latest/
If there is an Activity connected to the 'join a group' then you could use Scheduled Reminders.
Assuming there isn't then I think CiviRules extension may be the only non-code route.
For Drupal systems, you could use Webforms for the 'sign up' form and then use Webform to trigger the email.