Can I keep messages completely contained in my instance?

I’m a complete newbie as far as this app goes, and I’ve only had little exposure to mastodon.

I would like to use the app to post internal team news, but keep it completely within my instance (I have it hosted with a commercial company in Germany). Do I have to do something for that or do I simply have to make sure I keep my federated id to myself and not publish/use it somewhere public?