JavaScript is a versatile, high-level programming language primarily used to create interactive effects within web browsers, enabling dynamic content and user engagement.
React is a JavaScript library developed by Facebook for building user interfaces, particularly single-page applications, by breaking down the UI into reusable components that efficiently update and render as the data changes.
Together, JavaScript and React empower developers to build responsive and interactive web applications with a smooth user experience.
Next.js is a web development framework providing React-based web applications with server-side and static rendering.
Tutorials
For React, I recommend the https://react.dev/learn/tutorial-tic-tac-toe tutorial.
For Next.js, I recommend the https://nextjs.org/learn/dashboard-app tutorial.