This calculated field sums up all the story points of issue in an epic. The field only makes sense when displayed on an Epic issue type.
Create a new Calculated Number Field (by JWT) custom field and name it properly.
Providing a description will help you to identify what the custom field does but this step is optional
Add the field to the relevant view screens associated with an Epic issue type.
Remember: All calculated fields are read-only and cannot be manually updated on a create or edit screen.
Check the results
Once configured and added to an issue screen (of an epic), the result will look like this: