Gj Auto add user to a group

This may be a basis question.

I need to automatically add all users on the site into a GroupJive group based on the user's User Group. I tried to create the Auto item, but cannot quite understand the configuration details. What trigger would be the most appropriate? Is there a conditional required? Any other options necessary?

Additionally, if a members user group is modified, will the user be automatically removed from the GJ group?

Thanks