If you have any questions, i'd be glad answering them!
You submit all songs at once, you can put them in a folder and submit the folder, or a better way is to put them on Soundcloud/Youtube/among others then submit a link.
Also it's if your first Jam ever, don't fall in the trap (like I did for my first Jam and I think a lot of us did lmao): You have to create a project in your Dashboard before submitting it for the Jam