Living in the States has me genuinely frightened. I'm not so naive as to suppose it's not always been rough, but it's clear we've entered a qualitatively different era. The moderate wing of fascism has died, and barbarism is all that remains.
I want to fight back in a substantive way, even if it's small. I want to participate in institutions which protect the vulnerable, myself included. I don't want to lock my doors and peek out the windows, but I know better than to engage in adventurist, individual "resistance." I also don't want to be in a social club where we sit and congratulate each other on having the right opinions. I'm past wanting to be on the "right side of history," where I content myself with personally disagreeing with the nightmare we live in. Something needs to be done; the window for taking action is swinging shut.
I have almost no experience in organizing. I've attended a handful of protests which mostly felt like a venting of frustrations for everyone there. I've associated with a few comrades who had good intentions, but never accomplished much. That's about it.
How do I actually go about being a part of something effective?
Honestly any local org would be a good place to start. Even better if they have a social event where you can meet folks first. And it's totally fine if you don't want to continue with an org for any reason. Just find another that's a better fit.
But if you're looking for left or socialist orgs specifically, folks have already mentioned a bunch of good options: FRSO, PSL, IWW, etc. I know the IWW has regular organizer trainings, and I found that really helpful for getting exposed to and practice with organizing techniques.