How do I put users into 2 different groups?

Wow! I don't know why (or I know exactly why now), but it worked. Thank you thank you thank you!!!

Glad you finally got it working! Please don't hesitate to let us know if you should have any further problems. In short you're basically using a Conditional to check what they selected in the dropdown field. You then apply the usergroup of your choosing based off the matched value. There's lots of potential for Auto Actions so I recommend exploring the other actions and triggers as there's no telling what it can do for you (if you need explanation of what certain actions do don't be afraid to ask!).

I've sent you the CBSubs documentation for review (hope your email can handle large attachments?). Please note I removed your email address from your posts so you don't get spammed.

What's a 'user list', how do I create one, and what does it do for me?

Displays a list of your users (see "Members" in our login module at the top of the page) and search them (if configured). You can create them from CB > Userlist Management. See your CB documentation for further details (available for download in Advanced downloads section).

How do I put a similar "members" link on my page somewhere? Do I just do it through Joomla?

Create a Joomla menu link to CBs userlist page. You need to have a userlist though for it to do anything. You can add a new userlist from CB > Userlist Management.

How do I make a userlist of just specific user types (e.g. U2, U3, U4, not U1)?

And, how do I use CB Search Bot to search for just those user types as well (please elaborate)?