How could i submit my game through the jam or i have to submit it normally on itch.io???

You first upload your game to itch normally then you submit that to the jam.  You probably wont be able to see the jam submission until the jam actually starts in a few hours though. 

Yes you have to finish and upload your game to itch as normal first, once you've done that then return to the jam main page and press the big 'Submit your project' button at the top.  That should give you a list of all your games, just select the one you want to enter.  Don't forget you need to make the game public as well.