I feel like I must have missed something important, but I don't feel like I skipped anything.

It seems like everything is telling me to talk to Charlie to get setup. _How_ do I talk with Charlie?

I think I'm supposed to do that on an issue maybe? I'll try that.

Yes, once you've connected your GitHub (or Linear) then an issue is a good place to start talking to Charlie. Slack is good as well, but we typically do our meaty work through issues internally, since the conversation often evolves and Slack becomes a bit crowded for in-depth discussions.