To use MongoDB in your application, you need to connect your server to the database.

This is done using a connection string. It contains the information needed to access your database.

In Express applications, this connection is usually handled with Mongoose.

First, install Mongoose:

npm install mongoose

Then connect to your database:

const mongoose = require('mongoose');

mongoose.connect('your_connection_string')
  .then(() => {
    console.log('connected to database');
  })
  .catch((error) => {
    console.log('connection error', error);
  });

If the connection is successful, your server can now read and write data in MongoDB.