I am following these tutorials as I wanted to start with MongoDB and the MERN stack:
Try this It seems like you are using MongoDB atlas
mongoose
.connect( uri, { useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true })
.then(() => console.log( 'Database Connected' ))
.catch(err => console.log( err ));
and go to your MongoDB Atlas -> NetworkAccess-> Edit-> and add Current IP address it works!!