It's basically a contest in getting ideas. To enter the competition, you must pay the entry fee of 25 MB (25,000,000 Bytes) to the address shown in this post. You then simply create a blog post describing your idea, the way it can be realized, what the value of realizing the idea would be and so on. To learn more on how it could look like, please read the weekly reports we post every week. There are links to other contestants' blog posts describing their ideas and the progress they've made.
RE: Announcing the Steem Use-a-Thon by Byteball