Does Buddha go to Naraka (hell) to save those tormented beings? I heard one regarded by many a Buddhist teacher said, "Buddha will go to Naraka to save those suffering (tormented) beings, whilst those (monks, buddhists) will want to go to the Purelands. That (Buddha going to hell) is called Great Compassion."

Is this teaching correct, is it Buddha's teaching? I learnt that


One should bear one's own deeds and consequences (karma), neither a father could bear on behalf for the son, nor a daughter for the mother;
Buddha could not "give" enlightenment to anyone because enlightenment is reached by oneself; 
If one who hasn't cultivated enough merits, one would be born in one of the Eight Obscured Places (八無暇) that Dharma couldn't be heard; one of the Eight Obscured Places is Naraka.


Is this saying contradictory to 3)? Why is he saying this?
As far as my study in sutta, Buddha did not go to hell to help beings in that world.  They are considered to be "unfortunate" beings; among animals, hungry ghosts, and gods in arupa world because they do not have the strength or what it takes to understand dharma.  However, in one instance, Buddha was so kind to a Naga (which considered to be a being in animal world) by telling him to observe 8 precepts on Upasatha days and he would become human faster.  In one sutta, Buddha compared beings in hell to be like a person drowning in a cesspool not even a strand of hair above it to grab pulling him out.  

For question number 3) not always necessary.  In Migasala sutta, Buddha divided people into 10 groups, which one of them is;


  Here, ânanda, a certain person is overwhelmed with hate and from time to time greed arises to him. He has heard something fruitful, has learnt something, has straightened his view and he personally has gained some release. After death he does not go to loss gains some distinction.