Parent to child

In plain words: In Lightning Web Components (LWC), data flows down and events flow up . A parent passes data to a child through public @api properties, and can call a child's public @api methods. A child can't change the parent's data directly, so it sends a custom event with dispatchEvent , and the parent decides what to do with it. Real Salesforce apps are built from many small components that work together. To keep them clean and reusable, each component needs clear rules for how it talks to the others. This post covers both directions, parent to child and child to parent, using one simple example: a parent shows a product, and a child lets the user pick a quantity and add it to a cart.