There's guides on arena fighting to be found somewhere, like the T1, but i can't really find them at the moment. At its core it goes like this:
- Player 1 declares an attack by describing what he does and how he does it, but leaves it open whether or not the attack succeeds.
Example: Bob tries to punch Steve in the jaw with a right hook.
- Player 2 reacts to the attack. It's up to him to decide whether or not his character can (partially) avoid it or gets hit. If he gets hit, he also states the damage. Within the same post, player 2 can then make his attack, in the same way that player 1 did.
Example: Steve sees the punch coming so he steps to the left, avoiding it, and lashes out with his right foot to leg sweep Bob.
- These steps are repeated until one of the players is defeated.

There's a little more to it than that, but that's the basics. Because the defender decides whether an attack against them succeeds, a certain amount of trust is needed between participants in order to play fair. You can't control or assume someone else's actions, but you can make if-statements to react to things your opponent might do.
Example: Bob feigns doing a right hook. If Steve tries to block the punch, Bob makes use of the distraction by leg sweeping him.

Oh, and a charge is basically when you spend one or multiple turns not attacking in order to make a future attack more powerful. Sometimes charging keeps you from doing anything or sometimes you can still move and fight within certain restraints, it depends on the character.