Node.js is a JavaScript runtime built on Chrome's V8 engine. It's event-driven, non-blocking, and perfect for building scalable network applications.
Use require() to import modules, module.exports to export. Built-in modules include fs (file system), http (server), path (file paths), and os (operating system).
Express is a minimal web framework. Create routes with app.get/post/put/delete, use middleware with app.use(), handle errors with error middleware.
Handle async code with callbacks, Promises, or async/await. Use try/catch for error handling in async functions. Avoid callback hell with Promises.
npm install for dependencies, package.json tracks project metadata, node_modules stores packages, npm scripts automate tasks, use --save-dev for dev dependencies.