Node.js is an open source server environment which uses JavaScript on the server to develop backend applications
As you can see the definition itself describes that Node.js is all about JavaScript so your first step to Node.js should be Learning JavaScript
You can use these free resources to learn javascript: https://youtu.be/J4UKL355sUo
Once you are clear with JavaScript then next you can easily move forward to Node.js and its core concepts.
Follow this Structure to understand Node.js Concepts in proper way,
- Node.js Installation
- Node.js Modules: Node Package Manager (NPM)
- Http Server and Client: Express Framework, Routes, application Deployment
- Asynchronous Programming: Call stack, Callback queue and Event Loop mechanism
- Integration Of Node.js and MongoDB: REST APIs and GraphQL
- Authentication, Application Security and Testing
- Dynamic Client-Server Interaction and Microservices Application using Node.js
let me also give you some free sources to learn these Node.js Concepts:edureka Node.js - YouTube
Edureka’s Node.js Certification Training will help you gain the expertise in all the topics mentioned above
Also their Certification training is aligned with NCD program which is about to release in Mid of 2019- Certification - Node Foundation
You will be trained by Industrial Node.js Developers who have been currently working on any of the Node.js Projects
They do provide you assessments and project, where you can test yourself and cover-up your loop holes
Also their 24x7 support team is available, where the technical experts will help you clear your queries regarding the core concepts. Even they will guide you if you need assistance while solving the final Node.js Certification
To know more about Node JS, It's recommended to join Node JS Certification today.
I hope this helps you :)