Yeah, if you're not a good eventer, you won't be able to do anything really complicated with events, and if you need someone to explain it to you potential ways you could do it, you're probably not experienced enough to do it yourself even if someone explains it to you.
But think about a really simple battle system, like Rock Paper Scissors. How would you do that? Well, when it's the player's turn, you'd use a Show Choice branch. You could then save the player's selection to a variable Then, you'd go to the enemy turn. You'd set a variable to Rand 0...3. Then you'd have both of them having selected, so you'd then do a conditional branch for each possibility (Player picked Rock, Enemy picked Rock => 0 damage to either; Player picked Rock, Enemy picked Scissors => 1 damage to enemy, etc...). That would be a basic Rock Paper Scissors game.
Then, you could complicate things by maybe making the enemy not pick on equally random, but instead have it 50% likely that he picks rock over the other two - then you'd use rand (0...4) and distribute accordingly. And then you could make the damage different you could set variables to the enemy def and actor attack and make a custom damage formula. You could add graphics to it to make it a little snazzier - maybe play an animation on the sprite of an enemy.
The eventing gets complicated pretty quickly the more features you add; the more party members, etc... but roughly, that would be a process to making a battle system; have the player choose actions, save those actions, have the enemy choose their actions, save those actions, then define and enact the results. Repeat. You could also make a real time battle of course, but that becomes even more complicated. Basically speaking, in 2k3, you need to either know eventing, or have someone who knows eventing to make a good custom battle system. You'd probably want to get into picture eventing too if you wanted it to look at all pretty.
The long and short of it; learn eventing or recruit someone who knows how to event. Or else, move to a RMXP or RMVX and find a script for the battle system you want. Or: settle for the default battle system until you become familiar enough with eventing to do it yourself.