I assume you must be pretty new to essentials and rpg maker xp to ask a question like this
I would recommend the Pokemon Essentials wiki (can google for it) and some youtube tutorials (Thundaga is a content creator i believe makes good ones)
Additionally, you can roam around in the premade tutorial world Essentials comes with. It has a lot of tutorials to teach you how to do certain things
The wiki will have a bunch of detailed information on what certain parts of Essentials do, how to edit them, or how to use them
And a decent tutorial video series like the one i recommended should introduce a lot of this information at an introductory level
Including what youre asking now and a lot more