Server

The server software of Terraria is run in the game itself. To play on the server on the same computer as you run the server on, you need to start another instance of Terraria. You can then use "localhost" or your IP/hostname to join your server.

The server runs on port 7777. You will need to forward this port to your computer in order to let anyone outside your local network join the server. A maximum of 8 players can be in a world simultaneously.

Features
There are only a few features as of now. One is that you can drag the moon or the sun to change the in-game time of the server world. Also, the server will auto-save the world now and then.