Before you go
That is the whole thing. A public meeting is public. You do not register, you are not invited, nobody vets you at the door, and you are not expected to speak. Sitting quietly at the back with a notebook is a complete and legitimate act of citizenship.
The questions people do not like asking
No. Most people in the room never speak. There is usually a public comment slot, and you can ignore it. Watching and writing down what happened is the job.
Usually nobody says anything. Occasionally someone will be friendly and ask. "I live here and I wanted to see how it works" is a complete answer. You do not owe anyone an explanation for attending a public meeting, and you are not required to sign in — though some bodies pass a voluntary sheet around.
Whatever you wore that day. County commissions are not formal. You will be overdressed in a jacket.
Most run 30 to 90 minutes. Some are 15. If you need to leave, leave — people come and go and nobody minds.
In many states yes, and some open-meetings laws say so explicitly. But it varies, and a few places have conditions. Look up your own state's open meetings law before you point a phone at anyone. Written notes are never a problem anywhere.
You will not, at first. Nobody does. They use shorthand for things they have discussed for months. Write down the words you did not follow and look them up afterwards — by your third meeting most of it makes sense.
What actually happens
Once you have seen it once you will recognise it everywhere — county commissions, school boards, city councils and planning commissions all broadly follow this.
What to write down
Get the agenda beforehand if you can. Most bodies post one, and open meetings laws in most states require advance notice of the time, place and a tentative agenda. Reading it on the way in means you already know what to listen for.
Afterwards
Almost everyone finds the first meeting duller and less intimidating than they expected. That is the point. It is a room of people doing ordinary business, and the reason it matters is precisely that nobody is usually watching.
Pick one body and go back to it. Attending the same board repeatedly is worth more than attending six once: you start to see patterns, notice what keeps getting deferred, and recognise when something is unusual.