Using Mongo DB Atlas Account.
Add your connection URI at backend/.env file
git clone https://github.com/saurav90/mern-stack.git
$ cd mern-stack
$ npm install
$ cd backend
$ npm install
Go to backend directory and paste your atlas connection URI there.
ATLAS_URI = --Add Your Atlas Connection URL here -- (without quotes)
If you are using mongoDB in your local machine then use mongodb://localhost:27017/test.
For example: ATLAS_URI = mongodb://localhost:27017/test
$ npm run dev
This will start the backend express server and frontend react-scripts concurrently. You can also use two different terminals to start the frontend and backend separately
type npm start on mern-stack directory in one terminal and
type nodemon server on backend directory in another terminal