add a group on confirm email

I believe this will be an auto action but I am unsure where to start. 
When we get a new registration they have to confirm their email.  When that occurs or that action, I want to add a group to that user.

Can you help or point me to some documentation?
Thank you 

You want to add them to a group only after they've confirmed their email address? Yup, that's doable. The below should work using CB Auto Actions.

Global
Triggers: onAfterUserConfirm
Type: CB GroupJive
User: Automatic
Access: Everybody
Conditions
Field: Custom > Value
Custom Value: [var2]
Operator: Equal To
Value: 1
Action
Mode: Join Groups
Groups: SELECT_GROUP_HERE