For those who think playing this game online against other players is too hard, there is a way to play singleplayer against bots. It's not very straightforward. This article covers how to do it on the different operating systems:
http://my.bzflag.org/w/Single_Player_Mode
For the majority who use Windows, what you have to do is basically edit the shortcut to the game and insert the line "-solo 08" after the destination in the destination field. "08" is an example of the amount of bots you define in the game. So if you want 4 bots you should write "-solo 04" instead.
In the game itself you then need to start a local server and join that.