Learning back-end was one of the tougher challenges when it comes to programming. However, with the help of Meteor, I'm proud to say that I finally deployed an app that uses Node.js as backend and MongoDB as database: the Score Keep App (github). Try using this app on multiple devices and you will see that the data is synced in real time across devices. Granted this app doesn't have any user authentication and pretty much lacks any kind of security, but it's a step in the right direction.
Also, shout-out to Andrew Mead and his amazing course on Meteor. My app is based loosely on his course.