What is the meaning of the three slogans, "War is peace", "Freedom is slavery", and "Ignorance is strength"?

Each of these sayings seems contradictory and that feeds into the themes of the novel: freedom and enslavement, loyalty and betrayal, appearances and reality.  All of those are somewhat contradictory, too.  Orwell's book is meant to show what happens when absolute power corrupts absolutely which is what has happened in the world of the story.  The government has so much power over the people they can create their own reality which they have done.  The government of the fictional Oceania has a different interpretation of the slogans however.  For them, "War is peace" means that as long as they can keep the war machine moving, there is peace.  As long as they can keep people fighting the war and making implements with which to fight the war, then the people have no time to fight the government.  Therefore, for the government, there is peace.  "Freedom is slavery" is a bit more complex.  The Party (the government) is doing all it can to enslave the people, but it doesn't want them to think they are enslaved.  So, they brainwash the people.  They try to convince the populace that what some perceive as "freedom" is really nothing more than being tied to a doctrine which enslaves them.  Of course, the irony is obvious.  They are the ones with the doctrine that ties people to it. "Ignorance is strength" means that if the Party can keep the people ignorant of the truth then the Party is strong.  One of the main and one of the worst qualities of the Party is that it constantly rewrites history to suit its purpose.  That is, in fact, Winston Smith's job.  They keep people ignorant of the facts, they pump propaganda at them 24/7 and that keeps the Party strong. The Party wants people to see the slogan, however, as a way of consoling them to the idea that they, the people, don't need to be aware of all information.  They want people to see the Party as one who looks out for them and in doing so, takes on the burden of knowing what is good for them so the people don't have to be burdened with this information.  There is much more to each of these three slogans, I've only brushed the surface.  They are key to the novel and bear looking into further on your part.