Heads up! This blog post hasn't been updated in over 2 years. CodePen is an ever changing place, so if this post references features, you're probably better off checking the docs. Get in touch with support if you have further questions.
We hear people occasionally wondering out loud what they should tinker around building. CodePen is the perfect place for that, but the inspiration often comes frome elsewhere.
The app will straight up give you ideas, like:
Make a demo that calls different functions when the user holds down shift, alt, or ctrl/cmd and clicks a div
that are ranked by difficulty. Or it will show you a random Dribbble shot you can attempt to build. Or a random GitHub issue that might inspire something front-end-y.
In any case, it'll jump you over to a new Pen to get started with the basics.