handleAnEvent.html

<template>
  <div>{message}</div>
</template>

<script>
import { LightningElement } from 'lwc';

export default class EventHandlingComponent extends LightningElement {
    message;

    connectedCallback() {
        this.addEventListener('myevent', this.handleEvent);
    }

    handleEvent(event) {
        this.message = event.detail.message;
    }
}
</script>