JavaScript Express.js Server Not Working

Hello, I am currently working on Express.js on this page:

I tried to start up a local host server using the files from that Codecademy Express.js link (app.js, animals.js, expressions.js, and utils.js). However, I get an error that reads “Cannot GET /” on localhost:4001. I am using VSCode on Windows 10.

How could I fix this?

Thank you in advance.