The "Hand in"-button is only activated when you have uploaded a paper and all the required cover sheet information fields have been filled out.
Most often, cover sheet information still needs to be filled out to activate the hand in button.
Submission of a paper is only completed when you have pressed "Hand in" and the Hand in state is set to "Handed in", seen with green. See the example below:
Click "Send receipt" to have a receipt sent to the email associated with your account.