There are 3 types of adding Forms in add-on Forms & Checklist for Jira:
Automatic adding of Form to Jira issue is used for such situations when you need a certain form to be added immediately when you create a certain Jira issue type.
Manual adding of Form to Jira issue is used for adding a form or a few forms to a certain Jira issue by yourself.
(JSM) Customer portal adding of Form is used for adding a form to certain Jira tickets manually or automatically.