I just have a question on where is the "I am done button" stated here.
14. You can stop whenever you want to

You can click "I'm done for now" to end your voting session. The case that you stop on will not be counted and will jump back into the evaluation queue for other Tribunal members to vote on. http://na.leagueoflegends.com/tribunal/en/guidelines/

I have no clue where it at. Can i just quit when i log out or do i have to push that button ?

You can just exit or go to another page. The button used to take you back to the homepage, that was it.

oh i see. What will happen to the case i left ?

P.S. this wouldnt have a penatly on my account, would it ?

It stays there to be picked up next time you come back to the Tribunal I believe. I had a case where I had to leave my computer for about 20 minutes and when I came back and refreshed it took me to the Rules page to Agree again and then back to the same case.

Oh. Ok. Thanks a lot