Howdy mate!
On the main Greenlight Jam page, each of the four sprints (Ideation, Prototype, Production, and Polish & Release) have a link to a different itch.io jam page where the result from each sprint should be submitted one-by-one each week during the jam.
Use this link to submit your game concept for the first Ideation sprint. This will be a rough pre-production plan, including any ideas, concept art, storyboards, design docs or design pillars, mood boards, perhaps a plan of how the available time will be utilized in each subsequent sprint, a description of the tools you'll use, etc.
This first sprint phase will be a good opportunity to assemble teammates by pitching your concept to each other, with a comfy full-week to do it!
However, we will be launching a Discord server for this jam soon, which will serve as the ideal location for team formation, allowing for faster, more informal file and image sharing and easy informal pitching. I'll repost that server link when it goes live here!