Lightning Web Component(LWC) Components Communication in Salesforce

Communicate from child to parent
CustomEvent can be used.

Communicate from Parent to Child
The @api decorator in the child component exposes a property, making it public, so that the parent component can update it.
Similarly, @api decorator function in child component can expose it as public to call it from the parent component.

Communicate between Unrelated Components
Lightning Message Channel can be used.