First of all, head to https://cloud.mongodb.com , if you don't have a MongoDB account, then you should have an account first. We are not going to discuss the registration process as it is easy and you can create an account with your Github, or Google account.

Now, after signing in, you will be navigated to the dashboard or home page.

Inside the MongoDB logo, there is a box from where we can create a new project, Click on that!

Now, you will get options to enter the project name, go and fill that, and then click Next.

Hence, click on the big green button with text, Create Project.

After clicking on the button, it will take some time to create a project for you depending on the internet connection.

Its time to create a cluster.

After creating a new project, it will redirect you to a page where you can create a cluster, click on, Create.

Now, you have to deploy your cluster, you might see three options, M10, Serverless, and M10. We are going to use the free version as it is free and will be enough for our project. Choose on M10, write the cluster name, and click on create deployement.

Again, the navigated page will provide you two options: the first one is to add a connection IP address which will only allow to do actions with your cluster from the added IP and the second option is to create a database user in which you can create a new user which will gain an access to the created cluster with username and password.

Note: only added IP address and user will be able to access the project's cluster so choose wisely.

Now, close the dialog box, and come to the Databse tab after adding the user and an IP address.

Click on connect button, a dialog box will popup with the long connection string. It will look like this:
mongodb+srv://niraj:<password>@cluster0.dibosvc.mongodb.net/?retryWrites=true&w=majority&appName=Cluster0
where niraj = username, and <password> is the password for this user.

Now, after successfully getting the connection string, lets move to the mongoDB connection part.

  
  PORT=8000                 
  MONGO_DB_URI=mongodb+srv://niraj:<password>@cluster0.dibosvc.mongodb.net/?retryWrites=true&w=majority&appName=Cluster0
  # Make sure to replace the <password> with the real one
                

  
  export const DBName = "new-yt-mern-blog-app";
                

  
  import mongoose from "mongoose";
  import { DBName } from "../utils/constants.js";

  const connectDB = async () => {
    try {
      const connection = await mongoose.connect(
        `${process.env.MONGO_DB_URI}/${DBName}`
      );
      console.log(`Database connected: `, connection.connection.host);
    } catch (error) {
      console.log(`Mongodb connection failed `, error);
      process.exit(1);
    }
  };
  export default connectDB;
  

  
  import express from "express";

  const PORT = process.env.PORT;
  const app = express();

  import connectDB from "./connection/conn.js";

  connectDB();

  app.listen(PORT, () => {
    console.log(`Backend running on ${PORT}`);
  });
                

  
  ┌──(niraj㉿kali)-[~/…/js/reactjs/yt-mern-blog-app-new/backend]
  └─$ npm start    

  > backend@1.0.0 start
  > nodemon -r dotenv/config --experimental-json-modules app.js

  [nodemon] 3.1.4
  [nodemon] to restart at any time, enter `rs`
  [nodemon] watching path(s): *.*
  [nodemon] watching extensions: js,mjs,cjs,json
  [nodemon] starting `node -r dotenv/config --experimental-json-modules app.js`
  Backend running on 8000
  Database connected:  ac-q3o0xym-shard-00-01.v53dghk.mongodb.net