The "Local" timeline on your server shows all the latest public posts by people on your server. On Mastodon's web interface click 🌎 "Live Feeds" and select the "This server" tab.
You can also browse the Local timeline of most other servers, which can be very interesting if they're a themed server or well-run general server. Some apps also let you follow the Local timelines of other servers.
There's more info about all of this on the updated article at:
