Like Twitter, by default all of your posts will be public and may be federated to other Mastodon servers if their users follow you here. If you'd rather remain private, you can set your Post privacy options under Settings → Preferences → Publishing.
You can set privacy settings for an individual post at the time you make it by using the icon.
We won't be shy to suspend or kick troublesome accounts. Frankly, we've all got better things to do than deal with unnecessary shit on the internet, so if we see anyone generating unnecessary shit, they'll be in the bin pretty sharpish.
“Hang on,” you might be thinking, “isn't this all a bit subjective?” Well, yes it is. But by definition we're all grown-ups here. Use point 0 as your guiding principle. If it's possible that you're not being nice (or perhaps even being an asshole), don't say we didn't warn you.