You will be submitting through itch.io as usual:
When the jam enters the submission period people who want to enter the jam can navigate to the jam’s page to find a submit button. This brings up a game submission dialog where you can choose from games you've created on itch.io to submit. If you haven’t uploaded your game yet you'll be guided through the process.
Because jam submissions are itch.io project pages, you get all the features that itch.io provides. Your files and screenshots are hosted, and you can design a custom game page. A nice side effect of submitting to a jam on itch.io is that you automatically now have a nice page containing your game ready to be shared and distributed.