By looking at the code within Essentials, knowing what I wanted to do and how was it going to be gotten... If I wanted an Item to give me 75HP, I'd look at how Potions work... If I wanted a battle message at the start of the battle, I'd look into how PokeBattle_Battle, works... If you know what you want, you can access it through Essentials, online tutorials are complicated, the language in Essentials is clear.