A public server is a server which interacts with the list server and is able to be joined by players with typing in the address and port number.
To add your server to the list server you are first required to obtain an Authentication Key. This key links your account with being the owner of that domain, and you will have to provide that key in the Config File in order to successfully connect with the list server of 2.4.0. You can register your domain and get a key at http://my.bzflag.org/listkeys.
NOTE: Users switching from 2.0.x to 2.4.x servers will notice that the server authentication key was not an option at the time.
The public address that will be displayed to everyone is also required to have your server globally authenticate with the list server. This can either be your server's IP address, or a domain name. You may also include the port number if the default port number is not used.
-p 5154 -publicaddr myserver.org:5154
Unless you want your server to have no name, you can give your server a brief title that is displayed to everyone viewing the List Server. NOTE: Users switching from 2.0.x to 2.4.x servers will notice that the configuration option has changed from -public to -publictitle.
-publictitle "My Awesome Server - by My Name"
Verifying a Public Server
You may want to verify that your server is indeed going public. By enabling the -d option before starting the server, you can check the output to see if you are indeed hosting a public server. The output lines you should have may vaguely resemble:
Running a public server with the following settings: public address is sigonasr2.servegame.org:4500 LIBCURL version: libcurl/7.20.1 c-ares/1.7.1 Loaded master ban list from http://bzflag.org/master-bans.txt listening on 0.0.0.0:4500 with title of "My Awesome Server - by My Name"
As long as you are not seeing "private" server anywhere, you should be broadcasting to the world. This may not necessarily mean it is passing your firewall. See Creating a server for more details.