Does hell exist in Buddhism? I understand that hell is being used for keeping the order of our society. Does hell really exist in Buddhism?  As it creates fears instead of freeing one's mind from suffering. It also creates a mechanism of punishment for not believing in the religion as well.

If it is written in Tipitaka, how do we know that it wasn't added later by someone that wanted to use it as a  rule for making people behave themselves?
Does hell exist in Buddism?


Yes it does. It is a destination in which you mental state is painful and also painful mental states are sometimes called hell. Hell is mentioned in Bala Pandita Sutta. Painful mental states are compared to hell in Patala Sutta


  It also creats a machanism of punishment for not believing in the religion as well.


Buddhism is universal hence there is no notion of punishment. If a Hindu, Muslim, Christian does good then good results follow.

But having said that holding into wrong views does have consequences regardless if you consider yourself a Buddhist or not. 


  
    For one with wrong view, Lohicca, there is either of two destinies, I say, that is, hell or the animal womb. 
  


Source: (Sāla,vatikā) Lohicca Sutta


  It also creats a machanism of punishment for not believing in the religion as well.


If you look at the Abhidhamma associated the right view is belief in Karmic repercussions. Even Hindus can have it. Also to a certain extent people of other faiths if you believe an action has repercussions. This is not aimed at keeping you believing. Also right view does have shades and purity. The ultimate would be the experiential understanding but at a conceptual level the best understanding you can get is by reading Samma,ditthi Sutta.

Also Buddhism is not about any belief but experiencing the realities pertaining to our existance hence understanding the arising of stress and sorrow through whereby you can find a way out of it. You have to have some faith in the techniques as you would have to have in a doctor and his treatment to follow through with it.


  If it is written in Tipitaka, how do we know that it wasn't added later by someone that wanted to use it as a rule for making people behave themselves?


Vimanavatthu and Petavatthu was preached to make people understand reciprocation of Karma hence behave themselves. This also is not to keep someone tied to believe in the teaching. Also I do not believe this was added later.