What is Component?
The simple mean of Component is The Function that return HTML
const Button = () => <button>Click Me</button>;
What is JSX?
JSX (JavaScript XML) is syntax extension that allow you writing component in React/Next
Component in Next js
We have 2 Component in Next js, Client and Server Component. By default, all component in Next js App Router is Server Component
// This will be server component
const Button = () => <button>Click Me</button>;
So, how to create client component? Its simple! Just add "use client" on the top of page
'use client';
// This will be client component
const Button = () => <button>Click Me</button>;
Fyi, server component is only exist in Next js. So we havn't server component in React js
See full documentation about Server Component and Client Component