'How many fingers am I holding up, Winston?'
'And if the Party says that it is not four but five, how many?'
'Four.' The word ended in a gasp of pain."
In this quote, O'Brian is trying to manipulate Winston into thinking 2+2=5. Winston knows that is is not five and that freedom is to say that it equals four.
2) "'Who controls the past', ran the Party slogan, 'controls the future: who controls the present controls the past.'"
The Party's slogan says that since they control the present, they there for control the past. This is why they alter the past to make it appear that the party has been in control this whole time when they weren't.