I've got a basic idea of the game and have even bought a trail (right hand Marine), but I can't win any fights in Judo, Twinsword or Akido because everyone else has decent moves. Can anyone help me out on that front?

umm, well, im seeing as you just joined, just get used to all the available joints you have, and see what they can do. really, only experience makes u good in my opinion

Thanks, but like I've said I'm used to most of the joints (glutes and abs still confuse me)...

The glutes spread and unspread your legs.
(Ex.1 - Splits)

I'm sure he knows where do the joints move.
I bet he meant that when to do it. And "splits" isn't a good example, because I can easily make a split without even touching glutes.

But as engar10 said, you'll learn the use of every joint in time.
Play and practice! Beat tougher and tougher opponents! Win tournaments! Become the best!

I may not be the best to tell you what to do, but in my opinion defining yourself on "moves" is a bad idea. Better invent something new everytime you play, react to what you opponent does. it may be that some 1337ub3rpro has a two turns decap, but if you can grab his legs and crush them, he wont succeed.