Entry is easy. Simply go to the https://cardano.eco web page, scroll down and leave your idea in the comment section at the bottom. There are 5 prizes of 200 Ada each, and each user ID can enter up to 5 ideas. You can leave anonymous ideas and still win.
I hope this is fun and will be a learning event for me. Let me know any feedback if you like. Here is the associated YouTube video if you want more information.