There are currently two open spots left by Axel on PBW.
Carrier Battles #8, which currently has a big galaxy-wide war going on. Instant action, plus allies that will help you get a hang of the strategies and tactics being employed.
Carrier Battles Deluxe #2b is also open but since I'm not in it I don't know as much about what is going on. Almost certainly it will have a more stable political situation
You will probably want to read up on the tutorial page I have:
http://imagemodserver.mine.nu/other/.../CBmodTutorial