Once the game jam starts, you will need to come up with an idea for your game.  At the beginning, you won't have all the details worked out, but you can start building the basic concept.

I know that a lot of developers don't really like to do a lot of documentation and writing, but I'm going to suggest you write down your game ideas.  Once you have an idea that sounds promising, you can write short game concept document.

A game concept document is short, usually about 1 to 2 pages.  It's a high-level overview of the game, and much of the information can help potential players decide if they want to play the game.  Some information you will want to put in the document includes:

• Game title: What is the name of your game?  You can change it later, but if you're not sure at first, you can come up with a working title.
• Game genre: What genre is the game?  If you're not sure what a genre is, it's the type of game.  For example, some popular genres include puzzle, action, adventure, role-playing game, first-person shooter, and so on.  If you'd like to learn more genres, here's some recommended reading:
  • Game Development From Good to Great by Tony Floyd: https://www.amazon.com/Game-Development-Good-Great-Floyd-ebook/dp/B06VVN6JCT
  • Facet Analysis of Video Game Genres by Lee, Karlova, etc: https://www.ideals.illinois.edu/bitstream/handle/2142/47323/057_ready.pdf
• Platform: What device or platform is the game playable on?  Of course there can be more than one target platform.  Think about mobile devices, different computer operating systems, and consoles.
• Target audience and rating:  Who is the target demographic for this game?  Think about factors like age, gender, interest groups, and so on.  Basically, what kind of person would want to play this game?  If you were to sell this game in a store or marketplace, what kind of rating would it get?
• Game objective:  What is the player ultimately trying to achieve?  Is there also a purpose that you want to convey to the player (for example, do you want the player to learn something as part of the game)?
• Game concept/Elevator pitch:  If you had 30 seconds to describe your game to someone, what would you say? If you look at the description pages for games on the Google Play Store, Steam, and other marketplaces, or on the back of a physical game package, you'll usually see a short paragraph describing the game.  That's a good idea of what the elevator pitch should be like.
• Unique selling points (USPs): What makes this game stand out from others on the market?  Why should players choose this one over other similar games?
• Fun factor and features: When you look at the packaging or description page for a game, you'll usually see a bullet-pointed list of the game's highlights and features.  These items show the user what makes the game fun.  You might include some of your unique selling points in this list, and in fact, some people combine the USPs and the features, rather than having two separate lists.

As for most game and software documentation, there is no one set format for game concept documents.  Different developers might include variations on this overall format, with more or less information. 

A Real-Life Example

If you'd like to see an example of a concept document for one of my games, Brain Bouncer, you can view it here: https://www.slideshare.net/CloudyHeavenGames/brain-bouncer-game-concept-document.  And of course, you can play Brain Bouncer or view the project page at https://cloudyheavengames.itch.io/brain-bouncer.

So, having said all of that, here's my recommended action steps for you.

1. Check out the concept document I linked above, to see an example.
2. Choose a game that you like, or an idea that you have.
3. Write a game concept document based on the idea or game that you've chosen.  Keep in mind that throughout the game development process, you might make changes to your game, so it's ok to come back and change the initial document later.
4. If you'd like, you can share the document here, but don't feel pressured to.  I understand that if you have an idea that you want to develop, you might not feel comfortable sharing it with people yet.
5. Post here if you have any questions.