CodePen provides a very simple and easy-to-use interface for frontend web developers to test their code on the go and preview how their web app looks like. All the three files(HTML, JS & CSS) provided alongside each other make the user free from the hassle of switching between files. Along with the option to share your Pen on renowned platforms like GitHub, they also have a very vast & supportive community of their own where you can share your work & also like, review and even collaborate on pens shared by other users of the community. When I was in my learning phase of Web development, CodePen has helped me a lot! Watching tutorials is of no use if you don't get your hands dirty & try out the things, you've learned, on your own. CodePen is just the right platform to help you implement your skills & get real experience!

The most helpful material are hand made coding templates

I can check the outputs from all the languages in real time as I am writing the code in CodePen.