@eblu It varies a lot by where you are. What often works for radical communities is to find your local culture-focused squat, food-not-bombs effort, giveaway shop, clothes swap, something else that looks radical and has public events, and simply get talking to people and tell them that you've been looking for local community. There are event calendars on sites like radar.squat.net though your local anarchist/squat/punk/etc. scene may have their own thing too. Note that not every anarchist/radical group is necessarily very inclusive or open, so you may get a few duds.

If you're looking for a less radical community, other places to start include food banks (they almost always are looking for volunteers!), local churches doing homeless outreach (you'll want to check beforehand that they're not the sketchy kind), soup kitchens, and so on. There are also less obvious things in some places like "form-filling assistance" events where you might find like-minded people.

Generally speaking any kind of "helping others for free" thing is likely to welcome new hands to help, and that's the easiest way to get involved. Failing all that, it can be as simple as talking to your neighbours and trying to figure out who is (somewhat) receptive towards progressive views - they do not need to be radical, just open enough to progressive change to get along with them, though this can be harder to start with if you don't have pre-existing social connections.

Finally, don't underestimate what you might find in your local family and friends circle! Sometimes all you need is an idea for a thing to organize, however simple, as long as it is something that vaguely-close-to-you people can participate in.