Like Axel said, once the jam officially starts, you can submit your game through the jam page. A button will appear on the page for you to do so . You will need to upload your game to itchio first as a project and then publish its page and make sure that it's public. When you click the submit button, there will be some questions you will need to answer about your game and then you select which one of your projects you want to submit for the jam.
Also, congrats for joining your first game jam!