Okay kiddo, let's talk about something called the essive-modal case. In some languages, you can change the way a word looks to show how it's being used in a sentence. The essive-modal case is a change you might make to a word to show that it's doing something in a special way.
Think about when you're pretending to be a superhero. You might put on a cape to show that you're doing something heroic. That's kind of like what the essive-modal case does for words in some languages.
For example, let's say there's a word "cat" in a language that uses the essive-modal case. If you want to say "I'm playing with the cat," you might change the word "cat" to show that it's the thing you're playing with. You could add something to the end of the word so it looks different, like adding "en" to make it "caten."
This special form of the word "cat" with "-en" at the end is the essive-modal case form. It helps you show that the word "cat" is taking on a special role in the sentence. So, that's how the essive-modal case works, kid!