The tutorial explains all the parameters you need to use, which includes the conditions. We've several usage tutorials that you can find below.
www.joomlapolis.com/support/tutorials
In addition to those there are a few usage videos that you can find below.
www.youtube.com/playlist?list=PLp0puRITgC7McQcw0Sli1qfSUQGwmflzi
All inputs also have descriptions to describe what they do and in some cases provide example values.
CB Auto Actions is just a tool. By it self it does nothing. Without a usage configured it remains as just a tool. The above tutorials explain how to make sure of it through various usages; including the usage you're wanting. I'm not sure what more to advise as the usergroup based off field value already covers your requested usage.
If all you're wanting to do is change what usergroup they register in though and not be based off a field value you don't need any of this. You'd just change the "New User Registration Group" within Users > User Manager > Options of Joomla backend.