1. Modules: Node.js has a set of built-in modules which are used for various purposes such as networking, file system access, etc. For example, the ‘http’ module is used to create web servers.
2. Event Loop: Node.js is an event-driven runtime environment. It uses an event loop to process events and execute callback functions. For example, when a user clicks a button, an event is triggered and the event loop will execute the callback function associated with it.
3. Package Manager: Node.js comes with a package manager called ‘npm’ which is used to install and manage third-party packages. For example, the ‘express’ package is used to create web applications.
4. Callback Function: Node.js uses asynchronous callback functions to process events. For example, when a file is read, a callback function is executed once the file is read.