Express can connect to different types of databases. It can connect to NoSQL databases and RELATIONAL databases also. It connects very well with the two popular databases - MySQL and MongoDB. We will see to connect it to a MongoDB DATABASE next. 

First, we will go through the basic setup steps and create a new Node.js application by creating a directory and CHANGING to it. Then will initialize a package.json file with the npm init -y command.

Now, we will install the required package of express and also the package of mongoose. Mongoose is a package built for express applications, which makes it very easy to INTERACT with mongoDB databases. We will install them with npm i express mongoose from the command line.  

Now, create a file server.js in the root directory and add the below code in it. Here, we are first importing express and mongoose and after that using it in the app. We have also created a PORT and MONGOPORT variable with different values of 3000 and 5000. 

After that we are using mongoose.connect() to connect to the LOCAL MongoDB instance. If the connection is successful, we are showing a success message or else an error message. 

Lastly, we are listening to the connections at PORT 3000. 

Now, from the terminal run the command node server.js and we are successfully connected to mongoDB.