Such contests are shorter in time and have a smaller prize pool. For creators like you it means that your ideas do not have to be as formalized as they usually are. You can spend less time working on it: as soon as you have a bright idea, jump in and participate!
It is very easy: usually your entry will be required to have a short description of your idea and a key visual illustrating it, all on one single page.
The quality of execution does not matter; in some contests there will be even a template provided for you as a base for your entry.